Matthew Todd

Regulatory and Scientific Affairs

1220 L Street, NW

Washington, DC 

20005-4070 USA

Telephone: 202-682-8319

Fax: 202-682-8031

Email: ToddM@api.org

www.api.org

June 13, 2014

Mr. Chris Frantz

US EPA 

109 T.W. Alexander Drive

Mail Code: #143-05

Research Triangle Park, NC 27709

Re: EPA VOC/Methane White Paper on Oil and Natural Gas Sector Pneumatic Devices

Dear Mr. Frantz:

The American Petroleum Institute (API) appreciates the opportunity to provide feedback on EPA’s White 

Papers on Methane and Volatile Organic Compound (VOC) Emissions in the Oil and Natural Gas Sector.

On April 15, 2014, EPA released, for external peer review, white papers that focus on technical issues 

covering emissions and mitigation techniques targeting methane and VOCs from five separate emission 

sources. As noted in the Obama Administration’s Strategy to Reduce Methane Emissions, EPA will use 

the papers, along with the input from the peer reviewers and the public, to determine how to best 

pursue additional reductions from these sources. As described below, API does not believe additional 

methane controls should be required at this time. 

API represents over 590 oil and natural gas companies, leaders of a technology-driven industry that 

supplies most of America’s energy, supports more than 9.8 million jobs and 8 percent of the U.S. 

economy, and, since 2000, has invested nearly $2 trillion in U.S. capital projects to advance all forms of 

energy, including alternatives. Many of our members will be directly impacted by any policy decisions 

that may arise from this effort regardless of whether it informs either regulatory action by the federal 

government or states.

API provided technical feedback and expertise throughout the development of the New Source 

Performance Standard (NSPS) Subpart OOOO rule. Each source addressed by the white papers was 

considered for regulation during the development of the NSPS and EPA, ultimately, chose not to 

regulate them. While our understanding of emissions from oil and gas production continues to evolve,

the fundamental merits of requiring additional regulatory control of these sources is unchanged. As 

such, API continues to believe that no additional regulation of oil and gas production sources is 

necessary prior to the full implementation of the NSPS OOOO rule and a subsequent evaluation of 

emissions.
Page 2

Considering the potential for significant impact on our members that may arise from any policy decision 

stemming from the white papers, API has developed significant technical comments (see attached) to 

address a number of technical inaccuracies about the sources and the conclusions that have been 

drawn. Barring significant revision, API believes that the current white papers are simply insufficient to 

inform sound policy decisions and that simply posting comments on the current version will not result in 

an informed process. As such, API recommends the EPA take the following steps:

 Revise the white papers to correct any fundamental flaws or inaccuracies that were identified in 

response to peer review and stakeholder comment (e.g., improved source descriptions, 

improved understanding of emission quantification, misconceptions about emission mitigation 

options)

 Develop a response to comments document that clearly identify the changes the EPA makes to 

the revised white papers and explains the Agency’s rationale for those changes

 Identify emission studies in progress that will better inform EPA’s understanding of these source 

emissions and await the pending study reports

In recent years, there have been significant swings in the national emission estimates from oil and gas 

production sources, including those covered by the white papers, which indicate a necessity to continue 

collecting data to improve our understanding. Much of this learning will come from improved reporting 

under Subpart W of EPA’s Greenhouse Gas Reporting Program as well as current studies and others 

planned in the coming years, which involve taking direct measurements of the sources. EPA and industry 

would both be well served by allowing these studies to inform policy. 

Again, we appreciate the work by EPA to initiate these white papers and the opportunity to provide 

feedback on this effort. API and its members are dedicated to working with EPA to improve our 

collective understanding of these emissions and providing the technical operator experience that’s 

needed to do so. Recognizing the potential for these white papers to inform not only EPA but other 

government agency policy decisions, we request the opportunity to provide additional feedback to the 

Agency in response to any of our comments in advance. Furthermore, we again offer our experience and 

expertise as EPA moves into the policy evaluation phase of this effort.

Sincerely,

/s/

Matthew Todd

Cc: Peter Tsirigotis, EPA

David Cozzie, EPA

Bruce Moore, EPA
i

Comments on

Oil & Natural Gas Sector

Pneumatic Devices

by EPA Office of Air Quality Planning and Standards

June, 2014

Prepared by

The American Petroleum Institute (API)
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 13, 2014

ii

Table of Contents

A. Executive Summary ............................................................................................................... 1

1. Section 1.1.1 Pneumatic Controllers - Definition of the Source..................................... 2

2. Actions Controllers Can Take............................................................................................. 4

3. Section 1.1.2 Pneumatic Pumps - Definition of the Source ............................................ 6

4. Section 1.2.1 Pneumatic Controllers - Background ......................................................... 7

5. Section 1.2.2 Pneumatic Pumps...................................................................................... 10

a) Pneumatic Chemical and Methanol Pumps ............................................................... 10

b) Pneumatic Diaphragm Pumps.................................................................................... 11

c) Gas Assist Glycol Dehydrator Pumps ............................................................................. 11

B. Charge Questions: ............................................................................................................... 13

Charge Question 1................................................................................................................... 13

a) Missing Information:................................................................................................. 16

b) Missing Validation:.................................................................................................... 17

c) Missing Limitations Discussion: ............................................................................... 19

Charge Question 2 ................................................................................................................... 20

Charge Question 3 ................................................................................................................... 21

Charge Question 4 ................................................................................................................... 22

a) Pneumatic Controllers: ............................................................................................. 22

b) Pneumatic Pumps: .................................................................................................... 24

c) Pneumatic Controllers and Pumps in the ICF/EDF Study ........................................ 26

Charge Question 5 ................................................................................................................... 28

Charge Question 6 ................................................................................................................... 29

Charge Question 7................................................................................................................... 30

Charge Question 8 ................................................................................................................... 30

Charge Question 9 ................................................................................................................... 30

C. Conclusion............................................................................................................................. 31
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 13, 2014

iii

List of Figures

Figure 1: Continuous Bleed Controller........................................................................................... 3

Figure 2: Intermittent Vent Pilot.................................................................................................... 4

Figure 3: Integral Controller........................................................................................................... 6

Figure 4: Pneumatic Pumps ......................................................................................................... 10

Figure 5: Double Diaphragm Pneumatic Pump............................................................................ 11

Figure 6: Glycol Recirculation Pneumatic Pump.......................................................................... 12

Figure 7: Glycol Recirc Pump Schematic...................................................................................... 12

Figure 8: Mizer Retrofit................................................................................................................ 22
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 13, 2014

1

A. Executive Summary

The U.S. Environmental Protection Agency (EPA) has developed a draft document titled Oil and Natural 

Gas Sector Pneumatic Devices (hereinafter “the White Paper”) to, as stated in the Preface, seek input 

and solidify its understanding of the methane and volatile organic compounds (VOCs) emissions from 

leaks in this industry sector. The American Petroleum Institute (API) hereby submits its input and 

comments in this document.

The White Paper does not meet the goal of being a high quality technical document intended as a 

resource to inform EPA’s deliberations regarding emissions due to pneumatic devices. Rather than a 

robust compilation and analysis of available information, the White Paper appears to be a summary of 

the information sources referenced. In some instances, the summaries of the underlying sources are 

incomplete and information is incorrectly mischaracterized. There are misunderstandings and 

incorrect/inaccurate statements scattered throughout the White Paper. No discussion regarding the 

limitations of the underlying sources is presented in the White Paper and there is no critical analysis of 

the accuracy or validity of the underlying sources or the information summarized from them in the 

White Paper. The logic and underpinning evidence leading to the conclusions and assertions made in 

the White Paper is not clearly presented.

The White Paper needs significant improvement in content, organization, and data sources to be useful 

if is intended to inform EPA’s understanding and evaluation of potential options to reduce emissions 

from pneumatic devices. 

Following the public announcement that a white paper was being drafted on emissions associated with 

pneumatic devices, API submitted early feedback (March 2014) to EPA and those comments and 

presentation are attached for further consideration.

Highlights of key review comments discussed in more detail later in this document follow:

 Confusing terminology and descriptions of these devices, some of which has been complicated 

by industry’s own misuse of terms, is ubiquitous in the reports, studies, and emission mitigation 

claims. Tackling this is a critical first step.

 It is a common misconception that intermittent controllers cannot replace continuous bleed 

controllers. This is not correct. In most instances, a continuous bleed controller can be replaced 

by an intermittent vent controller regardless of the application. The choice of controller types 

for a particular application is dictated by the process needs/demands while ensuring safe and 

reliable operation. For most applications, intermittent controllers are the lower emission option 

than continuous bleed controllers. If the process can tolerate the inherent delay in response 

associated with a low-bleed continuous controller, a low-bleed continuous controller may, in 

limited situations, be a lower emission option. 
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

2

1. Section 1.1.1 Pneumatic Controllers - Definition of the Source

The definitions of: “natural gas-driven pneumatic controller” and “non-natural gas-driven pneumatic 

controller” in the White Paper are unclear, indicate a potential misunderstanding, and should be 

modified. The White Paper says: 

Natural gas-driven pneumatic controllermeans a pneumatic controller powered by 

pressurized natural gas. 

Non-natural gas-driven pneumatic controller means an instrument that is actuated using 

other sources of power than pressurized natural gas; examples include solar, electric, and 

instrument air.

1. It is not clear whether these definitions are specific to the controller itself or also include the enddevice that the controller acts on to modify a process condition. For example, controllers with an 

electric input and relays that convert an electric input signal into a pneumatic output signal to an 

end device are common.

2. The definition of “Non-natural gas-driven pneumatic controller” implies that the controller is 

actuated which is not a correct understanding. A controller converts an input signal, typically 

mechanical (e.g. float level) or electric (e.g. pressure transducer), into an output signal. The output 

signal is typically pressurized gas (including natural gas) or electric, to actuate an end device, 

typically a valve operator that opens or closes a control valve - either partially or fully. 

3. More appropriate definitions with additional clarity would be: 

a. Natural gas-driven pneumatic controller means an instrument that converts an 

input signal (mechanical, electric, etc.) into a natural gas pneumatic output signal 

to an end device. 

b. Non-natural gas-driven pneumatic controller means an instrument that converts an 

input signal into an output signal that is other than natural gas pressure to an end 

device. 

The White Paper definitions of the different types/designs of controllers introduce a third set of 

definitions that do not conform with the existing regulatory definitions in Subpart OOOOor Subpart W. 

These definitions are not technically correct, and do not provide additional clarity to mitigate the 

current confusion. These definitions would benefit from some changes to better reflect their emissions 

characteristics, add clarity and correct errors.

Continuous Bleed Controllers 

Continuous bleed pneumatic controllers are those with a continuous flow of pneumatic 

supply natural gas to the process control device (e.g., level control, temperature control, 

pressure control) where the supply gas pressure is modulated by the process condition, and 

then flows to the valve controller where the signal is compared with the process set-point to 

adjust gas pressure in the valve actuator. For the purposes of this paper, continuous bleed 

controllers are further subdivided into two types based on their bleed rate:
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

3

 Low bleed, having a bleed rate of less than or equal to 6 standard cubic feet per hour 

(scfh).

 High bleed, having a bleed rate of greater than 6 scfh.

1. Describing a continuous bleed controller as having “a continuous flow of pneumatic supply 

natural gas to the process control device” is both incorrect and confusing. The defining 

characteristic of a continuous bleed controller is that it bleeds gas to the atmosphere at a 

continuous rate determined by the supply gas pressure (fixed), the restriction-orifice (in the 

controller) diameter, and the gas specific gravity. The continuous bleed controller is the 

“process control device” which is not readily apparent in the definition and hence is confusing. 

2. In a continuous bleed controller the supply gas pressure is not modulated by the process 

condition -the supply gas pressure is fixed and the pressure of the gas to the end device (valve 

controller) is varied by the controller. The controller accomplishes this by partially or fully 

blocking the atmospheric bleed port to the extent that the rate of gas released to atmosphere 

is less than the rate of gas entering the controller through the restriction orifice hence causing 

pressure to build in the control loop (i.e., the controller, the tubing from the controller to the 

end device and the end device) which causes the valve actuator to move the position of the 

valve (Figure 1). The controller reverses this action by moving the block off of the bleed port 

(which is larger and has a higher flow rate capacity than the restriction orifice) which causes 

the pressurized gas in the control loop to once again bleed to atmosphere along with the gas 

entering the controller through the restriction orifice. Although the bleed rate of a continuous 

bleed controller temporarily decreases during actuation (bleed port partially or fully blocked) 

and temporarily increases during de-actuation (bleed port not blocked) the overall bleed rate 

per unit of time is essentially the rate that gas will enter the controller through the critical 

orifice. 

From the perspective of understanding emissions and functioning of a continuous bleed controller

a more appropriate definition would be:

1. Continuous bleed pneumatic controller: A 

pneumatic controller that does not have a 

mechanical barrier between supply gas and the 

end device. These units rely on a bleed port that is 

covered by a block or flapper to increase the 

amount of pressure sent to the end device (close 

the bleed port) or decrease the amount of 

pressure sent to the end device (open the bleed 

port). This type of controller continuously bleeds 

supply gas to the atmosphere when not fully 

actuating an end device (bleed port fully closed). 

For purposes of this paper, continuous bleed 

controllers are further subdivided into two types based on their bleed rate:

Figure 1: Continuous Bleed Controller
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

4

a. Low bleed, having a bleed rate of less than or equal to 6 standard cubic feet per hour 

(scfh).

b. High bleed, having a bleed rate of greater than 6 scfh.

Intermittent Vent Controllers

White Paper Definition: Intermittent pneumatic controller means a pneumatic controller that 

vents non-continuously. These natural gas-driven pneumatic controllers do not have a 

continuous bleed, but are actuated using pressurized natural gas.

1. An intermittent pneumatic controller is not “actuated using pressurized natural gas” as the 

definition states. An intermittent pneumatic controller controls the flow of supply gas to the end 

device (valve actuator) in order to raise the pressure and actuate the end device. The end device 

(valve actuator) is the component in the control loop that is “actuated”. 

2. The defining characteristic of an intermittent pneumatic 

controller is that it has a physical barrier between the supply gas 

and the end device, usually in the form of a small three way 

valve often termed a “pilot valve” or “pilot plug” (Figure 2). In 

response to an input signal (mechanical, electric, etc.) an 

intermittent pneumatic controller either 1) closes the vent to 

atmosphere and opens supply gas flow to the end device hence 

actuating the end device; or 2) closes the supply gas flow and 

opens the vent to atmosphere hence de-actuating the end 

device. 

3. When not required to de-pressure the end device, an 

intermittent pneumatic controller is designed to have near zero 

emissions to the atmosphere. 

From the perspective of understanding emissions and functioning 

of an intermittent pneumatic controller, a more appropriate 

definition would be:

Intermittent vent pneumatic controller: An intermittent vent controller has a mechanical barrier 

between the supply gas and the end device and does not allow supply gas and a vent port to both be 

open at the same time. This type of pneumatic controller vents gas periodically to de-actuate (depressure) an end device (valve actuator).

2. Actions Controllers Can Take

One common misunderstanding regarding pneumatic controllers is that on-off controllers are 

intermittent and throttling controllers are continuous bleed. Either a continuous bleed or 

intermittent pneumatic controller can function in an on-off or throttling service. The defining 

characteristic of a pneumatic controller in on/off service is that the controller is not required 

to hold an end-device in an intermediate position (i.e. at the end of a control cycle the 

Figure 2: Intermittent Vent Pilot
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

5

control-gas pressure to the end-device goes to zero). The defining characteristic of a 

pneumatic controller in throttling service is that the controller is required to control an enddevice in an intermediate position (i.e. the control-gas pressure to the end device is 

maintained at a pressure between atmospheric and supply pressure).

Combining the type of controller and the service yields a simple matrix that describes both 

continuous bleed and intermittent controller emissions in each service. 

Another common misunderstanding regarding pneumatic controllers is equating an intermittent 

controller with snap-acting action (as in the Subpart OOOO definition) or equating proportional action 

with throttling service. Snap-acting and proportional describes the type of action a controller in on/off 

service may take and does not have a great impact on emissions. Either a continuous bleed or 

intermittent pneumatic controller in on/off service can operate in a snap-acting or proportional mode 

dependent on its design. 

A snap acting on/off controller will never send a partial pressure signal. It will wait until the input 

parameter has reached a maximum value and then snap open and stay in that fully-open position until 

the input parameter reaches a minimum value and then will snap shut and an exhaust port will snap 

open. 

A proportional on/off controller will send a partial pressure signal as soon as the input parameter 

increases above a minimum and as the input parameter continues to increase, the rate that the 

controller sends gas to increase the pressure signal to the end device increases. A proportional on/off 

controller service will allow supply gas to increase the pressure signal to the end device until the 

differential pressure across the controller pilot plug is zero (i.e., actuation pressure equals supply 

pressure). If the process variable is satisfied prior to reaching zero differential pressure then the 

controller will shut off supply gas and open the vent without ever fully opening the end device and will 

vent slightly less gas than a snap-acting on/off controller. Proportional on/off controllers can be 

thought of as soft open and soft close actions. 

Snap acting on/off controllers tend to reposition end-devices open and shut very quickly which can 

cause serious process problems in some situations. Proportional on/off controllers tend to ease into a 
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

6

change of state with fewer problems with slugging and surging. It is important to understand that the 

type of pneumatic device used and the configuration of the action is dependent upon the process 

being controlled. 

Zero Bleed Controller

White Paper Definition: Zero bleed pneumatic controller means a pneumatic controller that 

does not bleed natural gas to the atmosphere. These natural gas-driven pneumatic 

controllers are self-contained devices that release gas to a downstream pipeline instead of to 

the atmosphere. 

Unlike a continuous bleed or intermittent pneumatic controller a 

zero bleed pneumatic controller does not use pneumatic supply 

gas from a reduced pressure supply source (Figure 3). Pneumatic 

supply gas to a zero bleed controller is taken from the process gas 

upstream of the controller at the process pressure. Introducing this 

new term in the White Paper ignores the Subpart OOOO Technical 

Support Document (TSD) which said “(3) self-contained devices 

release gas to a downstream pipeline instead of to the 

atmosphere”. “Self-contained” or “integral” is a far better term, 

especially since the terms “Zero Bleed” and “No Bleed” have been 

assigned to other concepts within current regulations (e.g., in 

recent Colorado regulations “No Bleed” controllers were defined 

as those controllers that use instrument air for actuation) or have 

been used historically to describe intermittent controllers which do 

not bleed gas continuously.

From the perspective of understanding the functioning of this type of pneumatic controller, a more 

appropriate definition would be:

Integral pneumatic controller means a pneumatic controller that is physically built into an end 

device, receives its supply gas untreated from the process being controlled, and exhausts excess 

supply gas back into the process stream without any gas exhausting to the atmosphere

3. Section 1.1.2 Pneumatic Pumps - Definition of the Source

The White Paper characterization of pneumatic pumps as: 

Pneumatic pumps are devices that use gas pressure to drive a fluid by raising or reducing the 

pressure of the fluid by means of a positive displacement, a piston or set of rotating impellers. 

Pneumatic pumps are generally used at oil and natural gas production sites where electricity 

is not readily available (GRI/EPA, 1996d). The supply gas for these pumps can be compressed 

air, but most often these pumps use natural gas from the production stream (GRI/EPA, 

1996e).

Figure 3: Integral Controller
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

7

This definition should be corrected in the paper. The inclusion of pumps “reducing the pressure of a 

fluid” is not correct - pumps increase the pressure of a fluid. Pneumatic pumps that drive “rotating 

impellers” are not believed to exist and certainly are not in common use in the Oil and Gas Production 

sector if they exist at all. The excerpts from GRI/EPA 1996e, although correct, are not complete with 

respect to gas-assist lean glycol pumps discussed later in the document. The primary energy source for 

these pumps is the high pressure “rich glycol” from the glycol/gas contactor tower on a glycol 

dehydration unit with natural gas used to supplement the energy scavenged. 

4. Section 1.2.1 Pneumatic Controllers - Background 

Due to the incorrect information provided in the White Paper background discussion regarding 

pneumatic controllers the entire section has been excerpted (italics) and comments incorporated into 

the section (non-italics). 

Pneumatic controllers are automated instruments used for maintaining a process condition 

such as liquid level, pressure, pressure differential, and temperature. In many situations, 

across all segments of the oil and gas industry, pneumatic controllers make use of the 

available high-pressure natural gas to operate control of a valve. 

Comment: Except for integral pneumatic controllers, pneumatic controllers do not use “high-pressure 

natural gas” in their operation. Instead, they use reduced pressure “pneumatic supply gas” which is 

generally in the 15 - 35 psig pressure range. Most end devices have a supply gas upper pressure 

limitation of 35 psig.

In these natural gas-driven pneumatic controllers, natural gas is released with every 

actuation of the valve, i.e., valve movement.

Comment: Natural gas is actually released on de-actuation of an end device when pressure is vented 

rather than on actuation. 

In some designs, natural gas is also released continuously from the valve control pilot. 

Comment: Continuous bleed controllers do not have a “pilot” which is a commonly used term for the 

small three-way valve in an intermittent controller. Please see the discussion of intermittent 

controllers and pilots provided above in these comments. 

The rate at which the continuous release occurs is referred to as the bleed rate. Bleed rates 

are dependent on the design and operating characteristics of the device. 

Comment: Bleed rates from a continuous bleed controller are a function of the size of the restriction 

orifice controlling supply gas flow into the controller, the supply gas pressure, and the supply gas 

gravity. Please see the discussion of continuous bleed controllers provided above in these comments. 

Similar designs will have similar steady-state rates when operated under similar conditions. 

There are three basic designs of natural gas-driven pneumatic controllers: (1) continuous 

bleed controllers are used to modulate flow, liquid level, or pressure, and gas is vented 

continuously at a rate that may vary over time;
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

8

Comment: Continuous bleed controllers can be used in throttling service to “modulate” a process 

parameter or in on/off service to fully actuate or de-actuate an end device. The rate of gas release only 

changes when the controller is actuating (decreases) or de-actuating (increases). The rate of gas 

release per unit time is essentially equivalent to the rate of supply gas entering the controller through 

the restriction orifice. Please see the discussion of throttling and on/off service provided above in these 

comments. 

(2) intermittent controllers release gas only when they open or close a valve or as they 

throttle the gas flow; 

Comment: Intermittent controllers only release gas when de-actuating an end device (releasing 

pressure to reverse a positive control action). This de-actuation may open or close a valve, partially or 

fully dependent on whether the controller is in on/off service or throttling service, and dependent on 

the configuration of the control loop -i.e. pressure to open or pressure to close. 

and (3) zero bleed controllers, which are self-contained devices that release gas to a 

downstream pipeline instead of to the atmosphere (EPA, 2011a).

As noted above, intermittent controllers are devices that only emit gas during actuation and 

do not have a continuous bleed rate.

Comment: As previously noted, intermittent controllers only emit gas on de-actuation rather than on 

actuation. 

Thus, the actual amount of emissions from an intermittent controller is dependent on the 

amount of natural gas vented per actuation and how often it is actuated. Continuous bleed 

controllers also vent an additional volume of gas during actuation, in addition to the device’s 

continuous bleed stream. Thus, actual emissions from a continuous bleed device also 

depend, in part, on the frequency of activation and the amount of gas vented during 

activation. 

Comment: The temporary bleed rate of a continuous bleed controller during actuation will be less 

than the static bleed rate. During de-actuation, the bleed rate will be temporarily higher due to 

bleeding both the gas entering the controller and the pressurized gas from the actuated end device. 

However, the temporary reduction during actuation and increase during de-actuation will balance each 

other with the result that a continuous bleed controller’s emissions per unit of time will be basically 

equal to the amount of gas that passes through the restriction orifice. At all times, a continuous bleed 

controller’s maximum emissions are capped by the amount of gas that can pass through the restriction

orifice.

As the name implies, zero bleed controllers are considered to emit no natural gas to the 

atmosphere (EPA, 2011a).

In general, intermittent controllers serve functionally different purposes than bleed controllers 

and, therefore, cannot replace bleed controllers in most (but not all) applications. 
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

9

Comment: This statement is incorrect. In most instances a continuous bleed controller can be 

replaced by an intermittent vent controller regardless of the application. The choice of controller types 

for a particular application is dictated by the process needs/demands while ensuring safe and reliable 

operation. For most applications, intermittent controllers are the lower emission option than 

continuous bleed controllers. If the process can tolerate the inherent delay in response associated with 

a low-bleed continuous controller, a low-bleed continuous controller may, in limited situations, be a 

lower emission option. 

Furthermore, zero bleed controllers are “closed loop” systems that can be used only in 

applications with very low pressure and therefore may not be suitable to replace continuous 

bleed pneumatic controllers in many applications.

Comment: Zero bleed controllers (integral controllers) are not limited to applications “with very low 

pressure” and can operate over a wide range of pressures provided that the pressure downstream of 

the controller is sufficiently lower than the pressure upstream of the controller for the controller to

function and allow upstream gas to discharge into the process flow downstream. Integral controllers 

source their pneumatic supply gas from the process pressure upstream of the controller and are not 

limited by the normal pneumatic supply pressure of 15 - 35 psig. They are common in high pressure 

applications. 

Non-natural gas-driven pneumatic controllers can be used in some applications. These 

controllers can be mechanically operated or use sources of power other than pressurized 

natural gas, such as compressed “instrument air.” Instrument air systems are feasible only at 

oil and natural gas locations that have electrical service sufficient to power an air compressor. 

At sites without electrical service sufficient to power an instrument air compressor, 

mechanical or electrically powered pneumatic controllers can be used. 

Comment: Instrument air systems are only economically feasible at sites where the pneumatic supply 

gas demand is sufficient to justify the capital and operating expense of an instrument air compressor. 

At single well sites this is rarely the case. 

Mechanical controllers are limited in the scope of applications where they can be used and are not 

common. Mechanical controllers have typically been limited to level-control applications because of 

the inherent difficulty in providing mechanical force to reposition a valve in other services. The amount 

of force required to reposition an end device is largely a function of differential pressure across the 

process side of the valve. As this differential pressure increases, the amount of force required to open 

the valve rapidly exceeds the force that can be provided through the buoyancy of a float. 

Consequently, mechanical controllers are limited to low pressure operations.

Electric controllers convert an input signal into an electrical output signal. Historically the output signal 

has been limited to solenoid valves in electro-pneumatic control loops. Only recently have electric enddevices become available in a form that can operate on low-power solar electricity and can eliminate 

the requirement for control gas in the control loop. As industry gains more experience with their 

reliability and safe functioning they may become more common. 
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

10

Figure 4: Pneumatic Pumps

Non-natural gas-driven controllers do not directly release methane or VOCs, but may have 

secondary impacts related to generation of required electrical power (EPA, 2011a).

Comment: This is correct, except for mechanical controllers.

5. Section 1.2.2 Pneumatic Pumps

There are two types of pneumatic pumps that are commonly used in the oil and natural gas 

sector: piston and diaphragm (GRI/EPA, 1996d ). 

Comment: There are three common types of pneumatic pumps that are used in the oil and gas sector 

rather than the two noted in the White Paper from the GRI/EPA 1996d reference. These three types 

of pneumatic pumps are: 1) Pneumatic chemical and methanol pumps (both piston and 

diaphragm gas ends); 2) Pneumatic diaphragm pumps; and 3) Energy scavenging gas assist pumps 

that pump lean glycol on glycol dehydrator systems where electricity is not readily available. 

These three types of pumps account for the vast majority of pneumatic pumps in field use, and 

are responsible for the majority of emissions attributable to pneumatic pumps. These pumps have 

very different uses and emission profiles, and function very differently. 

a) Pneumatic Chemical and Methanol Pumps

Pneumatic chemical and methanol pumps are widely used in the upstream oil and gas industry where 

electricity is not available. These types of pumps are generally used to pump fairly small volumes of 

chemicals or methanol (often 

measured in pints or quarts per day) 

into well-bores, surface equipment, 

and pipelines. They are typically 

plunger pumps with a diaphragm or 

large piston on the gas end and a 

smaller piston on the liquid end to 

enable a high discharge pressure 

with a varied but much lower 

pneumatic supply gas pressure

(Figure 4). The usage of these 

pumps, the volumes of fluid pumped 

and the discharge pressure (hence pressure multiplers) needed from the pump will vary between 

different areas, reservoirs, and from well-to-well although they will tend to be used semi-continuously 

rather than episodic. There is often a seasonal variation in the usage of these pumps as well (e.g. in 

colder production areas more methanol is generally pumped in winter to inhibit freezing and hydrates). 

Emissions occur when the gas used on the pump stroke is exhausted to the atmosphere to enable the 

liquid side of the pump to fill with liquid in preparation for another pump stroke. Emissions are a 

function of the amount of fluid pumped, the pressure of the pneumatic supply gas, the number of 

pressure ratio’s between the pneumatic supply gas pressure and the fluid discharge pressure, and the 

mechanical inefficiency of the pump. 
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

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Pneumatic “gas recovery” chemical/methanol pumps are available that discharge gas at a high enough 

pressure to use as fuel or to enable recovery. Manufacturer’s information regarding gas usage is 

available for pneumatic chemical and methanol pumps. The majority of pneumatic pumps in the 

Onshore Production sector are chemical and methanol pumps. 

b) Pneumatic Diaphragm Pumps

Pneumatic diaphragm pumps are also widely used in the upstream oil and gas industry where electricity 

is not available. They are generally used to move larger volumes of liquids per unit of time at lower 

discharge pressures than chemical/methanol injection pumps. Their typical uses include transferring 

bulk liquids such as motor oil, pumping out sumps, and 

circulation of heat trace medium at well sites in cold 

climates during winter months. They are designed with a 

diaphragm separating the gas and liquid sides with the 

liquid pumped by deforming the diaphragm with 

pneumatic gas (Figure 5). These types of pumps generally 

have a 1:1 liquid:gas pump pressure ratio. Emissions are 

a function of the amount of fluid pumped, the supply gas 

pressure, pressure multiples between the pneumatic gas 

pressure and the liquid discharge pressure, and the 

mechanical inefficiency of the pump. Emissions occur 

when the gas used in the pump stroke is exhausted to 

enable liquid filling of the liquid chamber side of the 

diaphragm. The usage of these pumps tends to be 

episodic when needed except for the pumps in heat 

medium circulation where they are typically used during 

the winter months in cold climes. The frequency of usage 

of these pumps and the volumes of fluid pumped will vary from area to area, operation to operation, 

and seasonally. 

c) Gas Assist Glycol Dehydrator Pumps

Figure 5: Double Diaphragm Pneumatic Pump
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Pumps on field dehydrator units where electricity is not available are typically gas-assist (often 

inappropriately termed “Kimray”) type pumps. These pumps are used to pump re-generated “lean” 

glycol from atmospheric pressure to the glycol/gas contactor on a glycol dehydrator unit. Since the 

contactor is typically at fairly high pressure the pumps must have the capability for multiple pump ratios. 

Consequently, they are more complicated than the chemical/methanol pumps discussed earlier as they 

“scavenge” energy from the high pressure (rich) glycol flowing from the contactor to the regenerator to 

provide the bulk of the energy needed to pump the lean glycol into the contactor. Energy loss through 

piping friction and mechanical inefficiency is “made-up” by assist gas at the contactor pressure (Figure 6 

and 7). Glycol dehydrator lean glycol pumps operate continuously when the dehydrator is in operation. 

Emissions are a function of the lean glycol circulation rate, the pressure of the contactor, and the model 

of the pump. The assist gas enters the “rich glycol” stream routed to the reboiler/regenerator and is 

emitted via the overhead vent from the regenerator distillation column unless control systems are in 

place. 

Emissions from gas assist glycol dehydrator pumps can be calculated using GRI-GLYCalc, a processs 

engineering program, or manufacture’s specification sheets. Emissions are a function of the lean glycol 

circulation rate, the pressure of the contactor, and the model of the pump. 

These pumps have two major components, a driver side and a motive side, which operate in 

the same manner but with different reciprocating mechanisms. 

Comment: It is not clear what “reciprocating mechanisms” refers to in this sentence. It is true that 

pumps differ in their designs.

Pressurized gas provides energy to the driver side of the pump, which operates a piston or 

flexible diaphragm to draw fluid into the pump. 

Comment: The pressurized gas does not “draw fluid into the pump”. After a pumping stroke the 

pump piston is returned to its prior position by a spring and the fluid chamber is filled at that time. 

Pressurized gas provides the energy to pump the fluid on the pumping stroke. For dehydration unit 

Figure 6: Glycol Recirculation Pneumatic Pump Figure 7: Glycol Recirc Pump Schematic
API Comments on Submitted to EPA

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lean glycol pumps with gas assist pumps (e.g. Kimray glycol pumps) the primary energy supply to the 

driver side of the pump is the high-pressure rich glycol from the contactor tower with energy loss made 

up via gas assist with contactor pressure gas. 

The motive side of the pump delivers the energy to the fluid being moved in order to 

discharge the fluid from the pump. The natural gas leaving the exhaust port of the pump is 

either directly discharged into the atmosphere or is recovered and used as a fuel gas or 

stripping gas (GRI/EPA, 1996d). 

Comment: It should be noted that the only use of pneumatic gas from a pump for stripping gas is 

on glycol units where a flash tank is installed downstream of the lean glycol pump and the flash 

tank gas (mostly pump assist gas) is used as stripping gas. Gas assist energy scavenger lean glycol 

pumps discharge the assist gas into the low pressure rich-glycol stream downstream of the pump 

where it is routed to the glycol reboiler/regenerator and the gas, along with absorbed water and 

hydrocarbons, are emitted from the reboiler distillation vent stack. Emissions from the reboiler 

distillation vent stack are typically, though not always, controlled using a condenser to recover 

condensable hydrocarbons. The non-condensable gas may be combusted in the glycol reboiler or 

other heaters, returned to the process by compression, or vented. 

The majority of pneumatic pumps used in oil and natural gas production are used for 

chemical injection or glycol circulation (GRI/EPA, 1996d). Pneumatic pumps used for chemical 

injection are needed in oil and natural gas production to inject small amounts of chemicals to 

limit processing problems and protect equipment. Typical chemicals that are injected into the 

process include: biocides, demulsifiers, clarifiers, corrosion inhibitors, scale inhibitors, hydrate 

inhibitors, paraffin dewaxers, surfactants, oxygen scavengers and hydrogen sulfide 

scavengers (GRI/EPA, 1996d). These chemicals are normally injected using pneumatic pumps 

at the wellhead, and into gathering lines or at production separation facilities (GRI/EPA, 

1996d). Pneumatic pumps, commonly referred to as “Kimray” pumps, used for glycol 

circulation recover energy from the high-pressure rich glycol/gas mixture leaving the 

absorber and use that energy to pump the low-pressure lean glycol back into the absorber 

(GRI/EPA, 1996e) 

Comment: It should be noted that the energy recovery lean glycol pumps also use gas assist from the 

absorber to make-up the energy recovery loss. 

B. Charge Questions:

Charge Question 1

Did this paper appropriately characterize the different studies and data sources that quantify 

emissions from pneumatic controllers and pneumatic pumps in the oil and gas sector?

Although the paper attempts to summarize the studies referenced it is not consistent, is 

confusing in spots, and is not complete. The paper lacks a table that summarizes the results of 

the studies referenced using consistent units. As it currently is configured it is difficult to 
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

14

compare data across the different sources referenced or parse the data from the exceptions and 

opinions. The White Paper does not include validation or analysis of the underlying information 

from the sources used. The White Paper would benefit from inclusion of tables similar to the 

following. 

Pneumatic Controller Emission Factors

Source Production Sector

Methane Emissions from the 

Natural Gas Industry (GRI/EPA 

1996c)

Continuous 

Bleed

Intermittent 

Vent Overall

scfh 

gas/controller

scfh 

gas/controller

scfh 

gas/controller

36.33 0.00 18.24 

Canadian Petroleum Association 

(Picard, 2992)

Throttling On/Off

scfh 

gas/controller

scfh 

gas/controller

3.92 8.88

Estimates of Methane Emissions 

from the US Oil Industry (ICF, 

1999)

Continuous 

High Bleed

Continuous 

Low Bleed

scfh 

gas/controller

scfh 

gas/controller

18.24 1.85

Inventory of US GHG Emissions 

and Sinks: 1990-2012 (EPA, 2014) 

Natural Gas Systems

Overall

potential scfh 

gas/controller

17.99

Inventory of US GHG Emissions 

and Sinks: 1990-2012 (EPA, 2014) 

Petroleum Systems

Continuous 

High Bleed

Continuous 

Low Bleed Overall

scfh 

gas/controller

scfh 

gas/controller

potential scfh 

gas/controller

16.51 2.60 7.49 

Inventory of US GHG Emissions 

and Sinks: 1990-2012 (EPA, 2014) 

Natural Gas and Petroleum 

Systems Combined

Overall

net scfh 

gas/controller

6.15 

Greenhouse Gas Reporting 

Program (EPA, 2013)

Continuous 

High Bleed

Continuous 

Low Bleed

Intermittent 

Vent

scfh 

gas/controller

scfh 

gas/controller

scfh 

gas/controller

37.3 1.39 13.5
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

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Measurements of Methane 

Emissions from Natural Gas 

Production Sites in the United 

States (Allen, 2013)

Continuous 

Low Bleed

Intermittent 

Vent Overall

scfh 

gas/controller

scfh 

gas/controller

scfh

gas/controller

5.1 17.4 11.2

Determining Bleed Rates for 

Pneumatic Devices in British 

Columbia (Prasino, 2013)

Continuous 

High Bleed

High Bleed 

Intermittent

scfh 

gas/controller

scfh 

gas/controller

9.199 8.744

Pneumatic Controller Emission Factors

Source Processing Sector Transmission/Storage Sector

Methane Emissions from the 

Natural Gas Industry 

(GRI/EPA 1996c)

Continuous 

Bleed Overall

Continuous 

Bleed Overall

scfh 

gas/controller

scfh 

gas/controller

scfh 

gas/controller

scfh

gas/controller

56.79 22 56.79 20 

Inventory of US GHG 

Emissions and Sinks: 1990-

2012 (EPA, 2014) Natural 

Gas Systems

Overall Overall

potential scfy 

CH4/plant

potential scfh 

gas/controller

164,721 19.82

Inventory of US GHG 

Emissions and Sinks: 1990-

2012 (EPA, 2014) Natural 

Gas and Petroleum Systems 

Combined

Overall

net scfh 

gas/controller

18.82 

Greenhouse Gas Reporting 

Program (EPA, 2013)

Continuous 

High Bleed

Continuous 

Low Bleed

Intermittent 

Vent

scfh 

gas/controller

scfh 

gas/controller

scfh 

gas/controller

18.2 1.37 2.35
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

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Pneumatic Pump Emission Factors

Source Production Sector

Methane Emissions from the Natural 

Gas Industry (GRI/EPA 1996c)

Diaphragm Piston Overall

scfh gas/pump scfh gas/pump scfh gas/pump

23.58 2.59 35.32

Canadian Petroleum Association (Picard, 

1992)

Overall

scfh gas/pump

13.92 

Inventory of US GHG Emissions and 

Sinks: 1990-2012 (EPA, 2014) Natural 

Gas Systems

Overall

scfh gas/pump

12.29

Inventory of US GHG Emissions and 

Sinks: 1990-2012 (EPA, 2014) Petroleum 

Systems

Overall

scfh gas/pump

12.42 

Greenhouse Gas Reporting Program 

(EPA, 2013)

Overall

scfh gas/pump

13.3

Determining Bleed Rates for Pneumatic 

Devices in British Columbia (Prasino, 

2013)

Diaphragm Piston

scfh gas/pump scfh gas/pump

37.2 20.9

Economic Analysis of Methane Emission 

Reduction Opportunities in the US 

Onshore Oil and Natural Gas Industries 

(ICF, 2014)

Overall

scfh gas/pump

32.7 

a) Missing Information: 

The White Paper does not include information from relevant sources readily available to EPA or 

complete information from the referenced sources. For instance: 

 The TSD for either of the relevant regulations (Subpart OOOO and Subpart W) or the 

industry and e-NGO comments posted on the Subpart OOOO docket are not included in 

the White Paper references or discussion. All of these sources are relevant to “the EPA’s 

understanding” of this issue.

 No manufacturer’s data or information, readily available for almost all pneumatic 

controller models and configurations and pneumatic pump models and services, is 

included in the White Paper analysis despite being the most complete information 

available. This is a major omission which should be addressed (the EPA/GRI 1996 study 

estimates use manufacturers information in part). 

 Table 2-1 in the White Paper does not indicate any pneumatic pump measurements 

collected as part of the Prasino study when the study reported measurements and data 
API Comments on Submitted to EPA

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for 184 pneumatic pumps. However, this measurement data is briefly discussed in 

section 2.2.4 of the White Paper. 

b) Missing Validation: 

The White Paper reviews of cited references appear to be simply an effort to provide a synopsis 

of the studies with no discussion of the validity of the study results. The White Paper missed an

opportunity to provide an analysis of the reliability of the data presented. For example:

 The Allen et al, 2013 study did not capture any pneumatic controller metadata (e.g., 

manufacturer, model, supply pressure, service, actuation frequency) for their 30 second to 

just over 2 minute measurement periods and were forced to discard any data for sites that 

operators did not report as all low bleed or all intermittent types in developing their 

“average” emission factors. The average study measured emissions and differences 

between the EPA emission factors for low bleed pneumatic controllers and intermittent 

controllers, shown in Table 2-8 of the White Paper, were based on 60 measurements and 

129 measurements respectively (189 total) rather than the 350 measurements noted in the 

White Paper. Additionally, the very short duration of the measurements almost certainly did 

not measure across an entire control (actuation=> de-actuation=> static=> actuation) cycle. 

For an intermittent controller measuring for these short time periods would either “miss” a 

de-actuation and return a zero emission result or measure just an actuation and grossly 

overstate the emissions per unit of time. For example, if a controller that actuates once 

every 10 minutes was measured for a 2 minute period that happened to include a deactuation, then the resultant volume attributed to 2 minutes would overstate the emissions 

by a factor of 5. Coupled with the statement in Appendix G of the study that “At some sites, 

however, the controllers that were observed to have emissions were selected for sampling.” 

it is likely that the reported emission factors are biased high - perhaps significantly. Despite 

the White Papers claim that the Allen et al, 2013 study did not include sampling times;

The sampling time for each controller was not specified in the study, 

detailed information regarding each measurement made is available on the study website at 

http://dept.ceer.utexas.edu/methane/study/datasets3.cfm in three separate excel files. The 

text of the study report and supplemental information indicate that only level controllers

(which tend to have higher valve actuator volumes) were measured, although some 

temperature controllers and pressure controllers are noted in the detailed information 

referenced above and appear to be attributed incorrectly as leaks rather than pneumatic 

controllers. If correct, this does not represent the full population of pneumatic controllers 

and hence the "emission factors" for the pneumatic controllers presented in the paper are 

not representative of the full population. There appear to be major shortcomings in the 

pneumatics portion of this study but that assessment is absent in the White Paper. API 

understands that additional study was undertaken to address these issues and EPA would 

be well served to await the results of this additional work. 
API Comments on Submitted to EPA

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 For the pneumatic controller measurements, the Prasino study called an R2value (i.e., a 

measure of the fidelity of the result to the data) of greater than 0.25 as “Positive”. As noted 

in the White Paper the “supply pressure coefficients have R2 values of 0.41 and 0.35 for high 

bleed and high bleed intermittent controllers, respectively. In common usage, R

2

values less 

than 0.70 are taken as “no correlation”, and many studies disregard values less than 0.80. 

Treating values of 0.25 as “positive” is incorrect.

 For pneumatic controller measurements, none of the studies clearly explain how they deal 

with zero-flow measurements/records or malfunctioning controllers. Failure to properly and 

consistently address questionable data leads to questionable conclusions in these studies. 

For example, assume there are 30 occurrences of a given make and model number 

controller for a one-hour test, and the measured data indicates the following:

Count Unit exhaust Population exhaust

20 0 0

7 0.2 SCF/hr 1.4 SCF/hr

2 99.0 SCF/hr 198.0 SCF/hr

1 205.6 SCF/hr 205.6 SCF/hr

Total 405.0 SCF/hr

Average 13.5 SCF/hr

A careful analysis of this data would indicate a properly functioning device having an 

emissions rate of 0.2 SCF/hr (with the 3 outliers having a mechanical issue that is not a 

function of the controller and should not be included in an emissions characterization), 

but a statistical average of the population would yield an emission rate of 13.5 SCF/hr. 

Since intermittent-device emissions are dominated by process-driven “events”, a better 

characterization would be 0.2 SCF/actuation since any other hour chosen would have a 

different population of zeros and 0.2 SCF measurements.

An example is the Prasino study data for a Fisher 4660 Hi/Lo Pressure Pilot. As 

background, a Fisher 4660 is a process safety under/over pressure protection device that 

holds a fail-closed valve open in normal operation and emits about 0.05 scf/hr 

(manufacturers data sheet) when not in an over/under pressure condition. These pilots, 

and similar ones by other manufacturers, are generally used on well-site separators to 

shut-in a well in the event of an unsafe condition. Thirty of these devices were 

measured in the Prasino study with 28 having zero or essentially zero emissions and two 

having measurable emissions and simply listed 0.0151 m3/hr (0.5 SCF/hr) as the 

“average bleed rate”. With knowledge of how these devices function it is obvious that 

either the two with emissions were damaged or malfunctioning in some manner or the 

process was in an overpressure/underpressure condition. However, the Prasino paper 

did not evaluate or include the reason for abnormal emissions and the White Paper 

failed to note this deficiency.
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c) Missing Limitations Discussion: 

The White Paper provides a synopsis of the sources cited with no apparent effort to highlight or 

discuss the limitations of these sources or their underlying origin. For example:

 The White Paper erroneously characterizes the US inventory; the GHGRP data; ICF 

Consulting, 1999; Roy et al., 2014; and ICF, 2014; as “studies”. Rather than studies, these 

reports are inventory estimates using emission factors and activity estimates often 

developed from reinterpretation or speculative analysis of the EPA/GRI, 1996 information 

and other data sources. An end result of an emission study (measurement) is developing a 

basis for assigning emissions factors to pneumatic controllers. The sources cited simply 

identified and applied an “emissions factor” to estimated device counts to reach an 

emissions number. 

 EPA/GRI, 1996 Study: The White Paper discussion of the EPA/GRI, 1996 study did not note 

that: (1) It is outdated, (2) There is insufficient information regarding actual measured 

controller emissions to evaluate whether the data is a good representation of the diverse 

population of pneumatic controller types, services, and applications; (3) There is insufficient 

information to judge whether the type of controller and service was correctly identified, (4) 

There is no information provided to judge whether the appropriate methodologies, sampling 

populations, and sampling times were used to adequately measure emissions from 

controllers. The EPA/GRI, 1996 data for pneumatic pumps has many of the same type of 

data-validation limitations. The EPA/GRI, 1996 data for Gas-Assisted Glycol Pumps is 

calculated based on two assumptions of process conditions, water removal, and information 

from Kimray. These process assumptions are significant limitations for the resultant 

emission factors derived in the report. 

 Greenhouse Gas Reporting Program (GHGRP): The GHGRP has required reporting of 

emissions from pneumatic controllers and pneumatic pumps since 2011 and data has been 

reported and publically released for 2011 and 2012. It is important to understand the 

limitations of this data and potential errors before using it for any purpose. The GHGRP 

divides pneumatic controllers into high-bleed continuous (>6scf/hr), low-bleed continuous 

(<6scf/hr) and intermittent categories. For each category the GHGRP has an emission factor 

(EF): These are: 

o Continuous low - bleed - 1.39 scf/hr; 

o Continuous high-bleed – 37.3 scf/hr; 

o Intermittent – 13.5 scf/hr. 

Reporters use a “count” of controller types in each category multiplied by the emission 

factor to estimate the volume of gas emissions for each category of controller in each 

“facility” (covered basin). For the 2011 and 2012 reports, these counts were allowed to be 

estimated using engineering judgment. For the 2013 emission year, to be reported by 

March 31, 2014, pneumatic controllers in each category are required to be counted. 

Obviously the accuracy of the reported emissions is contingent on the accuracy of both the 
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

20

emission factors and the counts of controllers in each category. With controller populations 

estimated for 2011 and 2012, the reported number of controllers is likely not accurate and 

the 2013 data should provide a much more accurate report of the population of controllers 

in each category. Given how an intermittent controller operates vs. a continuous bleed 

controller and very straightforward engineering calculations, the intermittent controller 

emission factor is likely very high – perhaps by an order of magnitude or more – hence, the 

emission estimates from this category are likewise high. Several studies soon to be 

published will provide some additional information to inform this question. Users of the 

GHGRP data for pneumatic controllers should wait for the 2013 reporting for a higher 

quality population count. Unfortunately, until the emission factors for each category can be 

validated and corrected, the GHGRP reported emissions for pneumatic controllers will 

remain highly uncertain. For pneumatic pumps the GHGRP uses a count multiplied by an 

emission factor to estimate the volume of gas emissions from each pump. In the GHGRP 

data, emissions from gas assist lean glycol pumps are included in the glycol dehydrator 

emissions rather than the pump emissions. 

 U.S. Greenhouse Gas Emissions and Sinks (Inventory): The National Inventory, which is 

updated annually, uses an estimate of the number of pneumatic controllers and an emission 

factor to estimate potential methane emissions for pneumatic controllers (called devices) for 

the “Natural Gas Systems” and “Petroleum Systems” categories by NEMS regions. 

Reductions in emissions attributable to Natural Gas Star voluntary taken and reported 

actions and regulatory required reductions (if required) are subtracted from these potential 

emission estimates. It is not clear what the genesis is for the pneumatic controller 

population estimate or emission factor hence it is not clear whether the estimate is valid or 

what uncertainty bands might apply. 

A similar approach is used for pneumatic pumps although the estimates in the NEI have 

activity factors and emissions separated from glycol process emissions for gas assist lean 

glycol pumps (called Kimray pumps in the NEI). 

Charge Question 2

Please discuss explanations for the wide range of emission rates that have been observed in 

direct measurement studies of pneumatic controller emissions (e.g., Allen et al., 2013 and 

Prasino 2013). Are these differences driven purely by the design of the monitored controllers 

or are there operational characteristics, such as supply pressure, that play a crucial role in 

determining emissions?

The majority of the differences between the two studies are more likely related to sampling 

times, methodologies, controller type identification, and data analysis assumptions rather than 

actual differences due to operational characteristics or actual differences in emissions. 

 For example, as discussed above, the UT Phase 1 study measured pneumatic controllers 

for very short periods, did not collect any metadata, likely misidentified the types of 
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controllers measured, concentrated measurement on level controllers which tend to 

have larger valve actuator volumes and, therefore, higher emissions from these 

intermittent vent controllers. The study also “screened” a large proportion of the 

controllers measured with an infrared camera and only measured those which were 

emitting which would likely bias the measurements towards continuous bleed or 

actuating intermittent controllers or intermittent controllers with some malfunction.

This would create a bias towards much higher emissions.

 The Prasino study purposefully concentrated on measurement of “high emitting” 

controllers and measured each for only a 15 minute period.

 Both studies used the measurement period and measured rate to extrapolate an hourly 

emission rate which for intermittent vent controllers is not a valid approach absent 

measurement across an entire control cycle and knowing the frequency of actuation. If 

a field experiment is connecting measurement equipment to a controller and running 

for 15 minutes, then if a device which actuates once a month happens to actuate during 

that 15 minutes it appears to be a high emissions rate. Any other 15 minute period 

during the month would show zero emissions. This means that if that particular 

controller in that particular stream vents 0.2 SCF/event and the vent event lasts 3 

seconds, some of the current studies would calculate a vent rate of 0.8 SCF/hr (0.2 

SCF/15 min * 60 min/hr) instead of the actual value of 0.00027 SCF/hr (0.2 SCF/730 

hr/month). The exact same combination of supply-gas pressure, controller, end-device, 

and tubing in another flow stream might operate twice an hour (actual value of 0.4 

SCF/hr), but may not have an actuation event during the selected 15 minutes. The study 

would show zero emissions even though its actual emissions rate in that service on that 

location is 1500 times larger than the controller that actuated once a month. 

The available underlying data from the various studies indicate that most controllers show zero 

emissions during the tests and that a small number of controllers showed very high emissions. It 

is not clear how the researchers accommodated both the zero emissions controllers and the 

obviously malfunctioning controllers in their estimation of emission factors. A careful, unbiased 

evaluation of the data would likely reach very different conclusions than were reached in any of 

the studies.

Charge Question 3

Did this paper capture the full range of technologies available to reduce emissions from 

pneumatic controllers and pneumatic pumps at oil and gas facilities?

Any list of mitigating technologies will by necessity be limited to currently available technologies. 

Equipment innovations for oil and gas operations are occurring continuously. For example, there 

has never been a viable low-power (solar power enabled) electric-actuated end-device for liquid 

removal (i.e., dump valve) until early in 2013 when such a device came on the market. The 

marketplace may very well broadly adopt this technology. Or users might find a fatal flaw that 
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

22

Figure 8: Mizer Retrofit

precludes its use in most applications. Any list of mitigation technologies that is included in 

regulations will likely stifle innovation at that point.

EPA should refrain from prescribing technology or attempting to specify solutions to engineering 

problems. Regulatory or policy approaches should enable industry to assess technologies to meet 

desired performance standards and make the appropriate and safe selections for each process 

need. 

One of the most prevalent emissions-reduction strategies in use today for pneumatic controllers is 

adapting continuous-bleed controllers to become intermittent-vent 

controllers via installation of a “pilot valve” (often termed a Mizer 

retrofit – Figure 8). This strategy has been very successful, widely 

reported by Natural Gas Star partners, and known to EPA but this 

strategy is not discussed in the White Paper. 

Charge Question 4

Please comment on the pros and cons of the different emission 

reduction technologies. Please discuss efficacy, cost and feasibility 

for both new and existing pneumatics.

The emissions-reduction technologies, the technical limitations on their applicability, and economic 

limitations are not clearly described in the White Paper. The costs for implementing a particular action 

or technology discussed in the White Paper are not on a current (2014) dollar basis, not presented on a 

consistent basis, and do not have the base year clearly noted for many actions or technologies. These 

deficiencies make it difficult to evaluate the White Paper’s cost estimates. A coherent strategy for 

reducing emissions from pneumatics or evaluating what such a strategy might cost cannot be

developed from the White Paper information. 

a) Pneumatic Controllers:

The information regarding technologies for reducing emissions from pneumatic controllers is 

primarily contained in Table 3.1 of the White Paper. Table 3.1 is replete with inaccuracies, 

misunderstandings, and naïveté. For example:

 Option: Install Zero Bleed Controller in Place of Continuous Bleed controllers. The devices that the 

White Paper describes as “zero bleed” use process gas for actuation and exhaust actuation gas 

downstream of the control valve. These devices require a differential pressure across the control 

valve and are only an option in a process which forces a gas pressure drop (i.e., pressure 

regulators and backpressure valves). Level control, temperature control, or flow control 
API Comments on Submitted to EPA

Oil & Natural Gas Sector Pneumatic Devices June 16, 2014

23

processes do not have the ability to use this equipment, but under Applicability, the White Paper 

states:

“Applicable only for relatively low-pressure control valves, e.g., in gathering, metering and 

regulation stations, power plant and industrial feed, and city gate stations/distribution 

applications (U.S. EPA, 2011a)”. 

These devices can be used in very high pressure applications, contrary to the only limitation provided 

in the White Paper.

 Option: Convert to Instrument Air:” The limitation on applicability of instrument air systems to those 

instances where reliable grid or integrated generator with backup emergency electrical power is available is 

not clearly stated. Also, the discussion of instrument air systems notes:

“In some instances, solar-powered battery-operated air compressors can be effective for 

remote locations, which reduce both methane emissions and energy consumption. Small 

natural gas powered fuel cells are also being developed.”

This statement is completely speculative with no references or demonstrated instances where 

this type of technology has been deployed and should be noted as such in the White Paper. 

The emissions associated with generation of electricity, often by coal powered power plants, should be 

taken into consideration when determining the potential emission benefits of instrument air systems.

 Option: Install Low Bleed Controller in Place of High Bleed Controller (U.S. EPA, 2006b). The historical 

approach for mitigating emissions from pneumatic controllers has been to replace continuous 

high-bleed controllers with intermittent-vent (often improperly called no-bleed controllers due 

to their near zero emissions between de-actuation events) or continuous low-bleed controllers. 

This practice remains a viable strategy for sharply reducing emissions from pneumatic 

controllers and should remain as a primary option. Note that replacement with an intermittentvent controller will typically provide the lowest emission solution with the widest process 

demand applicability. However, there are process control applications where either a lower 

emitting controller is not available or where the process demands require a continuous highbleed type and the option to continue use should be preserved. The White Paper does not 

adequately or clearly discuss the limitations on use of continuous low-bleed controllers inherent 

in their design that limits the amount of gas available for process control. Low bleed rates (<6 

scf/hr) are achieved by decreasing the diameter of the restriction orifice that controls the 

amount of pneumatic supply gas that can enter the controller and limits the rate that pneumatic 

supply gas can enter the controller. For a process application that demands more than 6 scf/hr 

to enable process control or demands process control at a faster rate (overall demand may be 

<6 scf/hr) than a continuous low-bleed controller can supply using a continuous low-bleed 

controller is not possible. Lower emissions and better control are generally available from 

intermittent vent controllers. 

 Option: Enhanced Maintenance. Under Description, the White Paper states
API Comments on Submitted to EPA

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“Instrumentation in poor condition typically bleeds 5 to 10 scfh more than representative 

conditions due to worn seals, gaskets, diaphragms; nozzle corrosion or wear; or loose 

control tube fittings.” 

To say that a worn seal, worn bleed port, worn restriction orifice, or failed diaphragm “increases 

emissions” is correct, but assigning “5 to 10 scfh” to that increased emissions is not 

substantiated and appears to be an opinion. Diaphragms do not “wear,” they hold pressure or 

they don’t hold pressure. A failed diaphragm can easily result in an exhaust rate that is an order 

of magnitude higher than “5 to 10 scfh”. Worn seals are unlikely to exhaust as much as 5 

SCF/hr.

 Option: Mechanical and Solar-Powered Systems in Place of Bleed Controller (U.S. EPA, 

2006a, U.S. EPA, 2006b): 

o Low power electrical controllers and actuators capable of running on a solar & 

battery electrical supply system are beginning to appear on the market. However, 

the availability of electric-powered controllers safe for use in flammable gas service 

and capable of meeting all process control needs is somewhat limited. Currently, 

the price on these controllers is several times that of an equivalent pneumatic 

controller plus the additional cost for an array of solar panels and batteries for 

reliable electrical power. Since they are fairly new, the range of available 

controllers is limited and their reliability and safety performance is not yet proven. 

Additionally, questions regarding the “fail safe” capabilities of these controllers and 

actuators have been raised. The manufacture of new batteries, and the subsequent 

generation of used batteries as a waste, should be taken into consideration when 

determining the potential emission benefits of solar-electric controllers and 

actuators.

o Mechanical controllers are limited to those level-control applications where the 

separator pressure is close to the water-exhaust pressure. If this differential 

pressure exceeds certain low value then the buoyancy of the float cannot provide 

enough force to move the valve.

b) Pneumatic Pumps: 

Unlike electric powered controllers and actuators discussed above, use of electric motor driven pumps 

is a mature technology that is widely and typically used when reliable electric supply is available. 

Electric motor driven pumps also tend to be more reliable and overall more energy efficient than 

pneumatic driven pumps. Conversion of pneumatic pumps to electric motor-driven pumps where 

reliable electricity is available should be the number 1 option listed in Table 3-5 and discussed in the 

White Paper. Conversion of gas-assist lean glycol recirculation pumps (a.k.a. Kimray glycol pumps) to 

electric motor driven pumps is the only option available and requires reliable electric power availability 

with greater power capacity than can feasibly be supplied by solar. 

Option 1: Replace natural gas-assisted pump with instrument air pump (U.S. EPA, 2011b) 

Section: 3.2.1 Instrument Air Pump
API Comments on Submitted to EPA

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The discussion of this option in the White Paper makes an incorrect and potentially hazardous 

recommendation of replacing the natural-gas assist for a lean glycol recirculation pump (a.k.a. Kimray 

glycol pump) with instrument air. However, in this type of pump the assist gas is discharged into the 

rich glycol flowing to the glycol reboiler/regenerator. Adding air (oxygen) to this stream could create 

an explosive mixture which is clearly not safe and could be potentially deadly. Additionally, adding 

air/oxygen would cause oxidation/degradation of the glycol and corrosion in the entire system which

would lead to premature failure. This section needs to be rewritten to eliminate this recommendation 

regarding natural-gas assist lean glycol recirculation pumps. 

This erroneous recommendation appears to have developed from a misunderstanding of the methane 

reduction project presented by the Natural Gas Star partner regarding “glycol circulation pumps” by 

the contractor that developed “Pro Fact Sheet 202” (referenced as U.S. EPA, 2011b) and a fabrication 

of the case study economic details in the Pro Fact Sheet. The project presented by the Natural Gas Star 

partner was a pilot project replacing natural gas powered pneumatic diaphragm pumps used to 

circulate hot glycol from the heated glycol-bath separator on well-sites around the well-site as heat 

trace medium to prevent freezing in winter. The pilot project had nothing to do with glycol 

dehydration or glycol dehydrator gas assist lean glycol circulation pumps. 

This example illustrates the critical necessity for the White Paper process to subject the underlying 

information sources and documents that the White Papers rely on to a rigorous and complete 

technical evaluation and validation. The White Papers should not rely on non-reviewed Natural Gas 

Star Lessons Learned, Pro Fact Sheets, and partner presentations. The documents underpinning the 

White Papers must be subjected to a valid technical review to provide credibility to this 

characterization of emission sources. 

Using instrument air rather than natural gas to power chemical injection and pneumatic diaphragm 

pumps is sometimes a viable option. However, the discussion in the White Paper presumes that an 

instrument air system with excess capacity already exists and that an operator would not have had the 

foresight to evaluate this possibility and would continue to use natural gas pressure (very inefficient) to 

drive the pumps – all of which is highly unlikely. If the White Paper is recommending installing an aircompressor, then the underlying assumption is that reliable electric power is available and it would 

certainly be more effective and efficient to electrify the pumping function than to install a new 

compressed air system. 

The White Paper discussion of replacing pneumatic chemical pumps with solar-powered electric 

pumps makes assumptions about maximum pressures and flow rates that came from a single case 

study in Natural Gas STAR. These assumptions were based on the subset of technology reviewed by 

the STAR partner at the time of the project and do not reflect the range of availability or limitations. 

The White Paper also notes that larger volume capacity solar operated pumps with high discharge 

pressures are available which is not a valid conclusion from the source cited (U.S. EPA, 2011b). 
API Comments on Submitted to EPA

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c) Pneumatic Controllers and Pumps in the ICF/EDF Study

The ICF/EDF study used the GHGRP data (discussed above) to adjust the 2011 inventory data for 

pneumatic controllers with the end result of a 41% increase in the 2011 baseline. Using the GHGRP 

data, the authors subdivided the population of pneumatic controllers into the three categories of 

continuous high-bleed, continuous low-bleed, and intermittent controllers; established the population 

of devices in each category, and used the GHGRP data to assign emission factors to each category. 

Using a series of assumptions the authors then subdivided the population of intermittent controllers 

into "dump valve intermittent controllers" and "non-dump valve intermittent controllers" with 

assumed different emission factors for each. Additionally, based on the API/ANGA survey report 

issued in September 2012, the authors added 23,000 pneumatic controllers to the number derived 

from the GHGRP data to account for pneumatic controllers at Gathering and Boosting stations which 

are not covered under the GHGRP. These additional controllers were subdivided into the three 

categories based on the GHGRP population distribution. The paper makes two recommendations for 

emission mitigation from pneumatic controllers:

 Replace high bleed controllers with low bleed controllers 

 Replace high-emitting intermittent controllers (not dump valves) with low bleed controllers

Given the uncertainty in the US Inventory, the uncertainty in the GHGRP data for pneumatic controller 

counts and emissions, and the additional uncertainty added by the authors assumptions, these 

recommendations need to be viewed with a significant degree of skepticism. 

As previously discussed, replacement of continuous high-bleed controllers with lower emission 

controllers is a well demonstrated approach to mitigating emissions from pneumatic controllers. 

However, the author's conclusion that the replacement should be done with a continuous low-bleed 

controller rather than an intermittent-vent controller is not a valid recommendation overall. 

Replacement of a continuous high-bleed controller with either an intermittent-vent or continuous lowbleed controller, where the process can tolerate the delay in response inherent to a low-bleed 

controller, is a more appropriate recommendation. 

The author's recommendation to replace "high-emitting intermittent controllers (not dump valves) 

with low bleed controllers" would likely result in higher emissions overall. As previously discussed, the 

GHGRP data (used by the authors to establish emission factors) for intermittent-vent controllers is very 

likely significantly overstated which would make the author's recommendation suspect from an 

emission reduction perspective. Also, the ability of the process to properly function with the slow 

response time inherent to a continuous low-bleed controller must be taken into account. There are 

cases where the slow response time can be tolerated and a continuous low-bleed device would be a 

lower emission selection. These instances demand a case-by-case evaluation and determination. 

The ICF/EDF methane mitigation paper conclusions for pneumatic pumps are even more suspect than 

the conclusions for pneumatic controllers. The ICF/EDF methane mitigation paper determines a count 

of 30,600 pneumatic chemical/methanol pumps and attributes this count to data reported into 

Subpart W and notes that this count is higher than the 28,000 pump estimate in the National 
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Inventory. However, the ICF/EDF count is not consistent with our estimate of about 84,000 pneumatic 

chemical/methanol pumps derived from the Subpart W data or the count of 63,715 pneumatic 

chemical/methanol pumps in the 2013 National Inventory. The White Paper does not clearly explain 

how ICF arrived at this significantly different count of pneumatic chemical/methanol pumps but it 

appears the count in the White Paper is incorrect and this should be indicative of the validity of the 

paper’s conclusions. 

Similar differences occur in the paper’s attribution of emissions from pneumatic chemical/methanol 

pumps.

 Table 3-2 attributes 5.9 BCF of emissions to pneumatic chemical/methanol pumps in 2018

 The discussion of pneumatic chemical pumps in Section 3.5 attributes 180 mcf of reduction per 

year to each pump replaced and notes that replacement of 80% of the pumps (presumably ICF’s 

30,600 pumps) was assumed for the analysis presented. Applying the described approach 

yields about 4.4 BCF/year in emission reduction from 80% of the pneumatic pumps considered.

 In the description of how the 2011 ICF baseline was computed, the paper notes application of a 

portion of the National Inventory reductions attributed to Kimray glycol dehydrator pumps to 

pneumatic chemical pumps but does not describe how this portion was determined. In Section 

3.1.8 the paper arrives at an “updated” increase in emissions from pneumatic chemical pumps 

of about 2% to over 3 BCF of gas

 Section B4.1.4 again notes the allocation of a portion of the “Gas Star” reductions to the 

National Inventory emissions from pneumatic chemical pumps (not allocated in the inventory) 

and notes a 30% decrease to just over 2 BCF of gas.

 Table 4.1 shows 4.8 BCF of methane reduced per year from pneumatic chemical pumps if the 

recommendations of the paper were applied. Applying the 80% replacement rate would imply 

total emissions of 6.0 BCF of methane which is close to the National Inventory pre-reduction 

emissions of 5.9 BCF of methane emissions from pneumatic chemical pumps. However this 

emission quantity occurs from a much smaller population of pumps in the paper. Also, whole 

gas emissions rather than methane emissions are the relevant measure to use in the analysis 

the paper purports to conduct. Using an assumed methane content of 85% (mole) the paper’s 

claimed reductions imply whole gas emissions of about 7.1 BCF which is close to the Subpart W 

data but again from a much smaller (30,600 vs. 71,000) number of pumps. 

The 180 mcf of whole gas reduction per pump replacement implies an emission rate of about 20.5 

scf/hr which is substantially higher than the 13.3 scf/hr in Subpart W or the 12.5 scf/hr (whole gas) rate 

derived from the National Inventory. If the stated reduction per pump is methane rather than whole 

gas, which is not clear in the paper, the emission rate would be about 24.2 scf/hr (whole gas) which is 

almost double the Subpart W and National Inventory emission rates. Given the paper’s 

representation of emissions from pneumatic chemical/methanol pumps that range from 2.0 BCF/year 

to 7.1 BCF/year coupled with the difference in the paper’s emission rates vs. the Subpart W and 

National Inventory emission rates, which are not explained in the White Paper, the conclusions of this 

paper need to be viewed with a high degree of skepticism. 
API Comments on Submitted to EPA

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The economics of pneumatic chemical pump replacement in the ICF/EDF mitigation paper are not 

clear. The paper reports using an initial cost of $5,000 per pump, $75 in annual operating cost, a 

recovery of 180 mcf of gas/year, a $4.00 gas price, and a 10% discount percentage. The paper does not 

report the replacement pump lifetime assumption or any component replacement assumptions (or 

lack of inclusion) in whatever lifetime was modeled. The paper concludes that replacing a pneumatic

chemical pump with a solar driven pump yields a positive return of $0.22/mcf of gas recovered over 

the life of the solar driven pump. A Net Present Value (NPV) analysis shows that reaching a “pay-back” 

value with the discount rate reported would take about 13 years while reaching the positive $0.22 

per/mcf of gas reduced would take about 17 years.

Although 17 years of solar pump system lifetime is likely valid for the solar panel portion of the 

systems; the battery pack, pump, and pump drive motor would likely have much shorter lives and 

require replacement at interim periods. Consequently, additional costs need to be added for 

replacement of these components which would lengthen the time necessary to reach the break-even 

point or the positive return noted in the White Paper. However, API is not aware of any information 

regarding the frequency of needed replacements as no/most solar powered chemical pump systems 

have been in place less than a decade. 

The above analysis is in stark contrast with the Section D.7 presentation of economics where the 

unnumbered table titled “Cost Benefit Analysis: Convert Natural Gas‐Driven Chemical Pumps” states a 

1 to 16 month payback. At 180 mcf/year recovered gas, $4.00 per mcf, and $5,000 initial cost, this

payback estimate is not correct, even based on the low cost estimates. A payback of the initial cost 

with no annual costs or discounting would take about 7 years. 

Also, by arriving at a smaller number of pumps responsible for essentially the same emissions as 

indicated by Subpart W and the National Inventory the White Paper, overstates the emission reduction 

benefit and the economic returns from replacement of pneumatic chemical/methanol pumps with 

solar powered pumps. If actual pump emissions are closer to the Subpart W emission rate then the 

economic benefits are overstated about 55%. 

In view of the internal inconsistencies of the White Paper regarding emissions, the obvious erroneous 

pneumatic chemical/methanol pump count, and the unrealistic economic payback periods claimed in 

the paper, the conclusions should be viewed as speculative. This paper should not be any part of the 

basis for any regulatory/policy initiative aimed at pneumatic chemical/methanol pumps.

Charge Question 5

Please comment on the prevalence of the different emission control technologies and the 

different types of pneumatics in the field. What particular activities require high bleed 

pneumatic controllers and how prevalent are they in the field?

API is not aware of any study or industry survey that documents the prevalence of solar electric 

operated controllers and actuators, solar electric powered chemical injection pumps, solar 

powered pneumatic diaphragm pumps, instrument air powered pneumatic controllers outside of 
API Comments on Submitted to EPA

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29

natural gas processing facilities, or instrument air or electric powered pneumatic pumps. There is 

some anecdotal information in the Natural Gas Star program information but it does not provide 

broad or complete information. However, the implication in this question is that the occurrence 

of such technologies/practices is an emission control technology rather than an appropriate 

engineering and economics choice for the particular application to oil and gas operations

An estimate of the numbers of intermittent vent, continuous bleed low-bleed, and continuous 

bleed high-bleed controllers can be derived from the 2012 GHGRP data by dividing the CH4 

emissions shown for each category by the emission factors in Subpart W and then correcting for 

methane content – which is similar to the approach taken in the ICF/EDF 2014 report. However,

this requires assuming that each controller operated 8760 hours per year and using the correct 

methane content to develop a count as the factors are in whole gas. Also, as discussed above, 

the 2011 and 2012 GHGRP counts of controllers in each category were allowed to be estimated 

by reporters based on engineering knowledge with an actual count required to be completed by 

the end of the 2013 emission year. The 2013 emission reports should provide a better basis for 

estimating controllers in each category due to the actual count underlying the emissions 

reported. In 2015, data reported for the 2014 emission year and prior years (2011, 2012, and 

2013) will include “deferred” data elements including controller counts in each category. This will 

eliminate the necessity to estimate a count from the GHGRP data.

Pneumatic pump counts can be estimated from the GHGRP data using the same approach 

described for pneumatic controllers and subject to the same limitations. Please note that gasassist lean glycol pumps are not included in the GHGRP data for pumps and are included in the 

glycol dehydrator emissions in the GHGRP data. 

The number of dehydrators with an annual throughput greater than or equal to 0.4 MMSCFD can 

be directly derived from the GHGRP data along with emissions for each such dehydrator 

reported. The emissions reported for each dehydrator can be used to determine whether the 

unit had a gas-assist pump or not. For dehydrators less than 0.4 MMSCFD, the count can be 

estimated by dividing the reported CH4 emissions by the Subpart W emission factor although this 

will not provide any way to distinguish the percentage of these units with gas-assist pumps. 

Charge Question 6 

What are the barriers to installing instrument air systems for converting natural gas-driven 

pneumatic pumps and pneumatic controllers to air-driven pumps and controllers?

Installing instrument air systems in field locations is limited to those instances where reliable 

electricity, most often from the grid, is available. Running small generators or small engines directly 

powering instrument air compressors and dryers is not reliable, demands much more maintenance 

resources, and has offsetting air emissions that make such an approach undesirable and not 

feasible. Solar arrays and battery systems necessary to power an air compressor are very large, 

expensive, and not used. From an economic standpoint, installing an instrument air system at a site 

where electricity is available depends on the pneumatic controller air demand being high enough to 
API Comments on Submitted to EPA

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30

make an installation economic – pumps will most likely already be electrically driven if electricity is 

available. In cold weather areas, instrument air systems require assured drying to prevent freezing 

which translates into oversized drying units and increased maintenance resources. 

As previously discussed, instrument air cannot replace the natural gas used in gas-assist lean glycol 

recirculation pumps. The only option for this type of pump replacement is an electric motor driven 

pump. Again, solar arrays and battery systems large enough to power these types of pumps are not 

feasible. 

Charge Question 7

Are there situations where it may be infeasible to use air driven pumps and controllers in 

place of natural gas-driven pumps and controllers even where it is feasible to install an 

instrument air system?

As previously discussed, instrument air cannot replace the natural gas used in gas-assist lean glycol 

recirculation pumps. The only option for this type of pump replacement is an electric motor 

driven pump. Again, solar arrays and battery systems large enough to power these types of 

pumps are not feasible.

Charge Question 8

Did this paper correctly characterize the limitations of electric-powered pneumatic controllers 

and pneumatic pumps? Are these electric devices applicable to a broader range of the oil and 

gas sector than this paper suggests?

Electric driven pumps are applicable to a broader range of applications than suggested by the White 

Paper where reliable grid electricity is available. Unfortunately grid electricity is not available at a 

majority of the individual well sites and a reliable, low cost, and clean method for generating the small 

amount of power needed does not yet exist. 

Process control loops, controller and valve actuator, powered completely by solar electricity are newly 

emerging in the marketplace. The range of available units is limited and the cost is several times that 

of an equivalent pneumatic controller. Most importantly, sufficient operational history has not been 

accumulated using such installations to broadly prove their reliability and safe operation. If they are 

found to work well, function reliably, and operate safely, the use is likely to increase, which will tend 

to push the prices down. 

Charge Question 9 

Are there ongoing or planned studies that will substantially improve the current 

understanding of VOC and methane emissions from pneumatic controllers and pneumatic 

pumps and available techniques for increased product recovery and emissions reductions?

API is aware of the UT Phase 2 study, with improved methodologies, that is measuring emissions from a 

wider population of pneumatic controllers and is due to be published later this year.
API Comments on Submitted to EPA

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In addition, API is aware of a study commissioned by Pioneer Natural Resources, one of the UT Phase 1 

and Phase 2 study sponsoring companies, which is reportedly planning to publish the results of an 

independent pneumatic controller measurement study in the near future. 

C. Conclusion

The White Paper titled “Oil and Natural Gas Sector Pneumatic Devices” represents a step backwards 

from the knowledge demonstrated in earlier EPA efforts (especially the Subpart OOOO Technical 

Support Document). The EPA would benefit from using the Subpart OOOO TSD as a starting point and 

commissioning a competent oil and gas engineering company with pneumatic controller and pump 

experience to assist in updating the TSD. While the TSD has significant errors and weak sections it is 

markedly closer to an adequate reference product than the “White Paper”.
API – March 24, 2014

Pneumatic Controllers

The category of pneumatic devices includes both pneumatic controllers and pneumatic pumps. These 

two types of pneumatic devices are very different and are discussed separately.

Pneumatic Controller Background

Process controllers are devices that sense a physical state and direct an end-device (typically a valve) to 

take an action to modify that physical state. These controllers can use a range of motive-force media 

such as pneumatic, hydraulic, or electric. Electric, hydraulic, and electro-hydraulic controllers do not 

release any gases to the atmosphere. Integral controllers that use gas directly from the process to 

increase actuation pressure and then exhaust excess gas back into the process to decrease actuation 

pressure do not emit. Pneumatic controllers that emit natural gas to the atmosphere, either 

continuously or intermittently, are the focus of this document. 

Pneumatic controllers may be the most misunderstood category from both an emission and proper 

classification perspective. This confusion is predominantly due to inconsistent use of terminology and 

use of different terms for the same type of controllers by industry, regulators, vendors, and others over 

many years. This has led to erroneous emission estimates, erroneous emission factors, and 

classifications of controllers that are not reflective of how controllers are designed, constructed, and 

used. 

From an emission perspective, pneumatic controllers that emit can be classified by a combination of 

their design type and the type of service they perform. 

The two types are: 1) Continuous bleed controllers: These are designed to bleed gas to atmosphere on 

a continuous basis and send a pressure signal to an end device (valve with actuator) by fully or partially 

blocking the bleed port. 2) Intermittent vent controllers: These are typically designed with a small 3-way 

valve (pilot) that sends a pressure signal to an end device on demand and vents actuation gas to reverse 

the action on demand. Between actuation/de-actuation cycles intermittent vent controllers are 

designed for near zero emissions.

The two services are: 1) On/off: The defining characteristic of an on/off controller is that the controller 

is not required to hold an end-device in an intermediate position (i.e. at the end of a control cycle the 

control-gas pressure to the end-device goes to zero); 2) Throttling: The defining characteristic of a 

throttling controller is that the controller is required to control an end-device in an intermediate 

position (i.e. the control-gas pressure to the end device is maintained at a pressure between 

atmospheric and supply pressure).
API – March 24, 2014

Combining the type and service yields the following matrix:

Additionally, on/off controllers can differ in the type of action taken and may either be snap-acting or 

proportional. Snap acting is often mistakenly used as an analogue for an intermittent controller or for 

an intermittent controller in on/off service. Proportional is often mistakenly used as an analogue for 

throttling controllers. Snap-acting and proportional describes the type of action a controller in on/off 

service may take and does not have a great impact on emissions. 

 A snap acting on/off controller will never send a partial pressure signal. It will wait until the input 

parameter has reached a maximum value and then snap open and stay in that fully-open position 

until the input parameter reaches a minimum value and then will snap shut and an exhaust port will 

snap open. 

 A proportional on/off controller will send a partial pressure signal as soon as the input parameter

increases above a minimum and as the input parameter continues to increase, the rate that the 

controller sends gas to increase the pressure signal to the end device increases. A proportional 

on/off controller service will only allow gas to enter the process until the differential pressure across 

the controller pilot plug is zero (i.e., actuation pressure equals supply pressure). If the process 

variable is satisfied prior to reaching zero differential pressure then the controller will shut off 

supply gas and open the vent without ever fully opening the end device and will vent slightly less gas 

than a snap-acting on/off controller. Proportional on/off controllers can be thought of as soft open 

and soft close actions. 

Snap acting on/off controllers tend to reposition end-devices open and shut very quickly which can 

cause serious process problems in some situations. Proportional on/off controllers tend to ease into a 

change of state with fewer problems with slugging and surging. It is important to understand that the 

type of pneumatic device used and the configuration of the action is dependent upon the process being 

controlled.

As shown in the table, both continuous-bleed or intermittent-vent controllers can be either snap-acting 

or proportional. Snap-acting or proportional action is not a defining function of a controller for the 

purposes of determining emissions.

Type of Service

On/Off Throttling

Type of Controller

Intermittent Vents on de-actuation with 

emissions near zero between deactuation cycles

Vents some gas pressure 

when valve needs to move 

towards closed

Continuous Bleeds continuously, rate slows 

while process is “on”, but average 

rate is ~constant

Bleeds continuously, rate 

varies with actuation, but 

average rate is ~constant
API – March 24, 2014

Emission Estimates and Studies:

Engineering Calculations

Time based emissions (e.g. scf/hr) from an intermittent controller in on/off service can be calculated 

based on the volume of gas needed to actuate an end-device (actuation volume) and the number of 

times the controller vents for de-actuation in the time period (cycles). The important parameters are 

the volume of the valve actuator, the length and diameter (volume) of the tubing from the controller to 

the valve actuator, the pressure of the gas signal to the actuator, and the frequency of actuation cycles. 

For example, an intermittent on/off temperature controller on a field heater that requires firing every 5 

minutes (12 times/hr), with an actuator volume of 1.1 cubic inches and 6 feet of 3/8 inch diameter 

tubing and a supply gas pressure of 25 psig would have emissions of ~0.18 scf/hr. An intermittent on/off 

level controller on a well separator producing 10 bbls/day of liquids that dumps 1.3 gallons per cycle 

(13.5 cycles/hr), with an actuator volume of 110 cubic inches and 10 feet of 3/8 in diameter tubing and a 

supply gas pressure of 25 psig would have emissions of ~2.6 scf/hr. 

Time-based emissions from an intermittent controller in throttling service are more difficult to calculate 

since the controller is holding a set-point and partially actuating/de-actuating an end device to partially 

open or close a valve. The volume vented per partial de-actuation is determined by the change in 

pressure in the tubing and actuator and the actuation volume and is much smaller than a full deactuation. However, the throttling controller would likely make adjustments somewhat more frequently 

and it is reasonable to use a percentage of the on/off controller emissions based on engineering 

judgment. Emissions will normally be less than an on/off controller in the same exact application. 

However, throttling controllers cannot be used in many process control applications.

Determining the number of cycles in a particular time period and the actuation volume for an average 

intermittent controller that is representative of the population of intermittent controllers and types of 

service is very difficult. Therefore, the development of an average emission per unit of time for the 

broad class of intermittent controllers will not accurately represent real world emissions unless a very 

large and broad set of data is accumulated. 

In contrast, continuous bleed controllers lend themselves to calculating a time-based emission rate due 

to their design. Continuous bleed controllers have a restrictive orifice that controls the rate that supply 

gas can enter the control loop and either bleed to atmosphere or be used in actuation and then added 

to the bleed on de-actuation. An emission rate can be calculated using a standard orifice calculation 

with the most important parameters being the orifice size, supply gas pressure, supply gas properties 

(gas specific gravity), and the tubing/passage size downstream of the orifice. For a continuous bleed 

controller with 20 psig supply gas, a specific gravity of 0.63, a 0.030 inch orifice, and 3/8 diameter tubing 

the bleed rate would be ~56.8 scf/hr. An orifice size of 0.010 inch would yield a bleed rate of about 6.3 

scf/hr with the other parameters held constant. Because continuous bleed controllers emit the 

actuation gas, in addition to the gas that passes through the orifice, their average emissions per unit of 

time is equivalent to the rate that gas will pass through the orifice. 
API – March 24, 2014

For both types of controllers malfunctions can occur which will change the emission profile. For an 

intermittent-vent controller, debris or deposits on the pilot ball (s) may affect the seat and cause higher 

emissions during the actuation portion of the cycle or during the idle portion of the cycle between 

actuation/de-actuation sequences. Both types of controllers can also have diaphragm, o-ring, and/or 

spring failures which may increase or decrease emissions with the effect dependent on the design of the 

individual device. Sufficient data to evaluate the frequency of these types of malfunction events and 

their materiality from an emission perspective is not yet available. 

Pneumatic Controller Information/Data Sources and Studies

EPA Question: What are the different studies and data sources that quantify emissions from pneumatic 

controllers in the oil and gas sector?

All information sources and studies should be carefully evaluated prior to use. Considering the 

confusion and mistaken information surrounding different types of pneumatic controllers and their 

emissions, this is critically important. For pneumatic controllers:

 All studies need to be evaluated to judge whether they are a good representation of the diverse 

population of pneumatic controller types, services, and applications.

 All studies need to be QA/QC’d to judge whether the type of controller and service was correctly 

identified. 

 All studies need to be QA/QC’d to judge whether the appropriate methodologies, sampling 

populations, and sampling times were used to adequately measure emissions from controllers.

 All studies need to be QA/QC’d to judge whether the data collected was appropriately analyzed and 

attributed.

Greenhouse Gas Reporting Program (GHGRP) and National Inventory of GHG Sources and Sinks 

(Inventory):

The GHGRP has required reporting of emissions from pneumatic controllers since 2011 and data has 

been reported and publically released for 2011 and 2012. It is important to understand the limitations 

of this data and potential errors before using it for any purpose. The GHGRP divides pneumatic 

controllers into high-bleed continuous (>6scf/hr), low-bleed continuous (<6scf/hr) and intermittent 

categories. For each category the GHGRP has an emission factor (EF): These are: Continuous low -

Bleed - 1.39 scf/hr; Continuous high-bleed – 37.3 scf/hr; Intermittent – 13.5 scf/hr. Reporters use a 

“count” of controller types in each category multiplied by the emission factor to determine the volume 

of gas emissions for each category of controller in each “facility” (covered basin). For the 2011 and 2012 

reports, these counts were allowed to be estimated using engineering judgment. For the 2013 emission 

year, to be reported by March 31, 2014, pneumatic controllers in each category are required to be 

counted. Obviously the accuracy of the reported emissions is contingent on the accuracy of both the 

emission factors and the counts of controllers in each category. With controller populations estimated 

for 2011 and 2012, the reported number of controllers is likely not accurate and the 2013 data should 

provide a much more accurate report of the population of controllers in each category. Given how an 

intermittent controller operates vs. a continuous bleed controller and very straightforward engineering 

calculations, the intermittent controller emission factor is likely very high – perhaps by an order of 
API – March 24, 2014

magnitude or more – hence, the emission estimates from this category are likewise high. Several 

studies (discussed below) soon to be published will provide some additional information to inform this 

question. Users of the GHGRP data for pneumatic controllers should wait for the 2013 reporting for a 

higher quality population count. Unfortunately, until the emission factors for each category can be 

validated and corrected, the GHGRP reported emissions for pneumatic controllers will remain highly 

uncertain.

U.S. Greenhouse Gas Emissions and Sinks (Inventory): 

The National Inventory, done annually, uses a single estimate of the number of pneumatic devices and a 

single emission factor to calculate potential methane emissions for pneumatic controllers (called 

devices) for the “Natural Gas Systems” and “Petroleum Systems” categories. Reductions in emissions 

attributable to Natural Gas Star voluntary taken and reported actions and regulatory required 

reductions (if required) are subtracted from these potential emission estimates. It is not clear what the 

genesis is for the pneumatic controller population estimate or emission factor hence it is not clear 

whether the estimate is valid or what uncertainty bands might apply. 

UT Phase 1 Study

This study, led by the University of Texas with support from EDF and 9 Oil and Gas Companies, sampled 

some 305 controllers with a paper published in the Proceedings of the National Academy of Sciences in 

mid-2013. Of the controllers measured, some 60 were identified as “low-bleed” and 129 as 

”intermittent” for a subset of 189 controllers where the type was noted. Based on the subset of 

identified controllers, the study concluded: Intermittent and low bleed pneumatic devices measured in 

this work averaged 5.9 ± 2.4 and 1.7 ± 1.0 g of natural gas per device per minute, 29% and 270% higher 

than EPA emission factors, respectively (SI Appendix, section S2). However, questions have been raised 

regarding whether the types of controllers (low-bleed or intermittent) were identified correctly and 

whether the sampling periods were long enough to reflect the variation of emissions from a controller 

throughout a single cycle and the length of a cycle. The UT Phase 2 Study is reported to be using 

improved methodologies for properly identifying pneumatic controllers and measuring emissions from 

pneumatic controllers. 

GRI/EPA 1996 study

This study was mostly based on manufacturer’s emissions information, site inventories/counts of 

pneumatic controllers, and engineering calculations. The study did include measurements of 19 

controllers made in a 1992 Canadian Association of Petroleum study and information provided by 

Chevron and Tenneco Gas Transportation. Despite the age of the data and the small 

sample/measurement set this study is still used as the basis for many emission estimates for the 

industry. 

Canadian Association of Petroleum Producers 2002 & 2003

The CAPP 2002 report concluded that the emission factor for an average pneumatic controller was ~7 

scf/hr which was based on information from measurements made in Alberta. This report did not 

distinguish between types of controllers or types of services.
API – March 24, 2014

2013 Prasino Report

The Prasino group published the results of a pneumatic controller measurement study conducted on 

behalf of the province of British Colombia and a consortium of producing operators in December of 

2013. This study intentionally focused on “high emitting” controllers where the manufacturers emission 

rate was greater than 0.119 m3/hr (~4.2 scf/hr). However, during the measurement campaign 

controllers with lower manufacturer’s rates were also measured. During the measurement campaign,

some 581 individual controllers spread amongst 15 model numbers plus one “other” category were 

measured. Average emission rates for each model measured were determined and reported. These 

ranged from ~0.5 scf/hr to ~14.8 scf/hr. The author’s determination that R2values above 0.65 

represented a “strong” correlation and over 0.25 a positive correlation does raise concerns. The 

underlying raw data for this study has been requested to enable a more robust analysis. 

UT Phase 2 Study

The UT Phase 2 study, with improved methodologies, is measuring emissions from a wider population of 

pneumatic controllers and is due to be published later this year. 

Pioneer Natural Resources Study

Pioneer Natural Resources, one of the UT Phase 1 and Phase 2 study sponsoring companies, is 

reportedly planning to publish the results of an independent pneumatic controller measurement study 

in the near future. 

Intermittent, Snap-acting, Continuous Bleed, and Throttling Controllers

EPA Question: Are there significant emissions from snap acting (intermittent) pneumatic controllers?

As discussed above, snap-acting is descriptive of a type of action an on/off controller may be configured 

to take, can apply to either continuous bleed or intermittent controllers, and is not an analogue for 

intermittent. Similarly, throttling describes a type of action an on/off controller may be configured to 

take and is not an analogue for continuous bleed. 

Emissions from an intermittent controller occur when the actuation volume is vented to reverse the 

actuation action. Emissions per unit of time are dependent on the volume per actuation cycle and the 

number of actuation cycles in the unit of time. In most applications, an intermittent vent controller, 

which does not bleed between de-actuations, is the low emission option. However, if an intermittent 

controller is in an application with a large actuation volume and frequent actuations it can have greater 

emissions per hour than a low-bleed continuous controller. Replacing such an intermittent controller 

with a low-bleed continuous controller to lower emissions is only possible where the process control 

demands can tolerate the delay inherent in the design of a low-bleed controller. For instance, a lowbleed controller (6scf/hr) in level control service with a 110 cubic inch valve actuator (typical for a 2” 

valve in medium/high pressure service), 10 feet of 3/8” tubing, and 25 psig pneumatic supply gas will 

take about 58 seconds to reach 5 psi and begin moving the controlled valve and about 116 seconds to 

fully actuate the valve actuator to the supply pressure of 25 psi. If the process cannot tolerate this scale 

of delay, then replacement of the intermittent controller with a low-bleed continuous controller is 

precluded. This type of determination requires a case-by-case evaluation and operators need to have 

the flexibility to use the type of controller needed for safe and reliable process control. 
API – March 24, 2014

Pneumatic Controller Emission Mitigation

EPA Questions: What are the technologies or practices available to mitigate emissions from pneumatic 

controllers? What are the pros and cons of the different options, including efficacy, cost, and feasibility?

Instrument Air and Electric

Using instrument air rather than natural gas as the pneumatic supply gas will eliminate gas emissions 

while providing the same level of process control. However, most well sites are remote from electrical 

grid supply to operate a compressor and drying system and instrument air systems are not feasible. 

Where grid electricity is available, sufficient demand for pneumatic air must exist to make an instrument 

air system cost effective. Instrument air systems, like any mechanical system, do experience failures and 

reliability needs to be taken into account as well. Additionally, drying of the instrument air is critical to

prevent freezing in the process control systems which cause failures to occur. Most gas 

processing/treating facilities, offshore platforms, and larger sites (such as compressor stations) with grid 

electricity or on-site electrical generation have instrument air systems for pneumatic services. Where 

grid electricity is available and sufficient air demand exists, instrument air systems should be evaluated. 

Where grid electricity is available, electric-powered controllers and actuators can be used rather than 

pneumatic systems – which eliminates emissions. However, the availability of electric-powered 

controllers safe for use in flammable gas service and capable of meeting all process control needs is 

somewhat limited. Low power electrical controllers and actuators capable of running on a solar & 

battery electrical supply system are beginning to appear on the market. Currently, the price on these 

controllers is several times that of an equivalent pneumatic controller plus the additional cost for an 

array of solar panels and batteries for reliable electrical power. Since they are fairly new, the span of 

available controllers is limited and their reliability and safety performance is not yet proven. 

Additionally, questions regarding the “fail safe” capabilities of these controllers and actuators have been 

raised. The manufacture of new batteries, and the subsequent generation of used batteries as a waste, 

should be taken into consideration when determining the potential emission benefits of solar-electric 

controllers and actuators. 

Lower Emitting Pneumatic Controllers 

The historical approach for mitigating emissions from pneumatic controllers has been to replace 

continuous high-bleed controllers with intermittent-vent, often called no-bleed controllers due to their 

near zero emissions between de-actuation vents, or continuous low-bleed controllers. This remains as a 

viable strategy for sharply reducing emissions from pneumatic controllers and should remain as a 

primary option. Again, there are process control applications where a lower emitting controller is not 

available or where the process demands require a continuous high-bleed type and the option to 

continue use should be preserved. 
API – March 24, 2014

ICF/EDF Paper: Economic Analysis of Methane Emission Reduction Opportunities in the U.S. Onshore 

Oil and Natural Gas Industries 

The ICF/EPA paper prominently notes two important caveats which need to be kept in mind:

 The 2011 EPA inventory is the best starting point for analysis, but it is based on many 

assumptions and some older data sources. Although the inventory is improving with new data, it 

is designed to be a planning and reporting document and is imperfect, especially at the detailed 

level, for a granular analysis of this type. 

 Emission mitigation cost and performance are highly site specific and variable. The values used 

here are estimated average values.

This study adjusted the EPA’s 2011 inventory based on the GHGRP data and UT Phase 1 studies along 

with some of the author’s assumptions and opinions which introduces significant uncertainty in 

addition to the GHGRP and UT Phase 1 study data uncertainty discussed above. The authors then 

“grew” the inventory to a 2018 projection using a series of projections and assumptions which adds 

additional uncertainty. Additionally, the authors “adjusted” the emissions projections, both in the 2011 

baseline and 2018 projection, for individual source types which adds uncertainty at the individual 

source type level. The limitations the authors note, the additional uncertainties introduced by the 

adjustments made to the 2011 baseline, the assumptions and methodologies used in “growing” the 

inventory to 2018, and the adjustments to individual source type emissions need to be considered

carefully in use of this papers conclusions.

In determining the mitigation costs for a particular practice, technology, or action the authors adjusted 

EPA’s and the State of Colorado’s economic analyses based on their opinions and assumptions which 

adds uncertainty on top of the inherent uncertainty in the EPA and Colorado analyses. 

Pneumatic Controllers in the ICF/EDF Study

The ICF/EDF study used the GHGRP data (discussed above) to adjust the 2011 inventory data for 

pneumatic controllers with the end result of a 41% increase in the 2011 baseline. Using the GHGRP 

data, the authors subdivided the population of pneumatic controllers into the three categories of 

continuous high-bleed, continuous low-bleed, and intermittent controllers; established the population 

of devices in each category, and used the GHGRP data to assign emission factors to each category. 

Using a series of assumptions the authors then subdivided the population of intermittent controllers 

into “dump valve intermittent controllers” and “non‐dump valve intermittent controllers” with 

assumed different emission factors for each. Additionally, based on the API/ANGA survey report issued 

in September 2012, the authors added 23,000 pneumatic controllers to the number derived from the 

GHGRP data to account for pneumatic controllers at Gathering and Boosting stations which are not 

covered under the GHGRP. These additional controllers were subdivided into the three categories 

based on the GHGRP population split. 

The paper makes two recommendations for emission mitigation from pneumatic controllers:

 Replace high bleed controllers with low bleed controllers

 Replace high‐emitting intermittent controllers (not dump valves) with low bleed controllers
API – March 24, 2014

Given the uncertainty in the US Inventory, the uncertainty in the GHGRP data for pneumatic controller 

counts and emissions, and the additional uncertainty added by the authors assumptions these 

recommendations need to be viewed with a significant degree of skepticism. 

As previously discussed, replacement of continuous high-bleed controllers with lower emission 

controllers is a well demonstrated approach to mitigating emissions from pneumatic controllers. 

However, the author’s conclusion that the replacement should be done with a continuous low-bleed 

controller rather than an intermittent-vent controller is likely not a valid recommendation overall. 

Replacement of a continuous high-bleed controller with either an intermittent-vent or continuous 

low-bleed controller, where the process can tolerate the delay in response inherent to a low-bleed 

controller, is a more appropriate recommendation.

The author’s recommendation to replace “high-emitting intermittent controllers (not dump valves) with 

low bleed controllers” would likely result in higher emissions overall. As previously discussed, the 

GHGRP data (used by the authors to establish emission factors) for intermittent-vent controllers is very 

likely significantly overstated which would make the author’s recommendation suspect from an 

emission reduction perspective. Also, the ability of the process to properly function with the slow 

response time inherent to a continuous low-bleed controller must be taken into account. There are 

cases where the slow response time can be tolerated and a continuous low-bleed device would be a 

lower emission selection. Again, these instances demand a case-by-case evaluation and determination. 

Conclusion

Overall, choices of specific controller types to replace continuous high-bleed controllers need to be 

made by the operators, after evaluation and analysis of the demands of the process system and the 

likely emission outcome based on actual knowledge of the process and controllers rather than a series 

of uncertain assumptions. Also, as previously noted, there are cases where the use of high-bleed 

continuous controllers are necessary and cannot be replaced with another type. 

Recommended Charge Questions for Peer Reviewers

1. Are assertions made in the paper supported by the underlying facts and data?

2. Are assumptions made in the paper clearly noted? Do these assumptions seem valid and 

balanced?

3. Do the data sources and studies that the paper relies upon appear credible and complete?

4. Was sufficient QA/QC conducted with regard to the data sources and studies that the paper 

relies on to determine their applicability and validity?

5. Does the paper adequately discuss the constraints inherent in a low-bleed continuous 

controller’s delay in initiating a control action and the consequent constraints on where they 

can be used?

6. Does the paper reflect an understanding of the limited instances where replacement of an 

intermittent controller with a low-bleed continuous controller is a lower emission option? 

7. Does the paper present a realistic evaluation of actual emission reduction potential from 

additional regulation of pneumatic controllers?

8. Are the conclusions reached by the authors supported by the information and data that was 

relied upon?
Pneumatic Controllers
Common Misconceptions 

2

 Intermittent controllers emit at a higher rate than low 

bleed (Subpart W)

 Low bleed controllers are the best overall choice

 Emissions also occur at the valve actuator

 Controller terminology is standardized and commonly 

understood

 That snap-acting, on/off, no-bleed, & intermittent are 

synonymous terms

 That throttling, continuous bleed, and proportional are 

synonymous terms
Goals 

 Seek common understanding of pneumatic controllers

 Types of pneumatic controllers

 How they operate

 Expected emission profiles. 

 Seek common understanding of key principles

 The choice of controller types for a particular application is dictated 

by the process needs/demands while ensuring safe and reliable 

operation

 For most applications, intermittent controllers are the lower 

emission option than continuous bleed controllers

 If the process can tolerate the inherent delay in response associated 

with a low-bleed continuous controller, a low-bleed continuous 

controller may, in limited situations, be a lower emission option

3
Process Control Systems

4

 A process control system/loop must have:

 A way to sense the state of a process variable (Float, pressure transducer, etc.)

 A way to change the state of the sensed process variable (Pneumatic Supply Gas, 

Controller, Actuator, and Valve)

 Process variables most commonly controlled in upstream Oil & Gas are:

 Fluid level (often found on separators, tanks, treaters, etc.)

 Pressure (includes pressure regulating, back pressure regulating, and overpressure limiting)

 Temperature (includes tank heaters, indirect process heaters, direct process 

heaters, and fan control)

 Differential pressure (often used as a surrogate for flow, generally used for 

constant flow processes)

 Position (includes devices that sense plunger arrival in a well and signal enddevices to allow after flow and/or to shut off the flow to allow the plunger to 

drop)

 Safety – Unique Category (includes control of emergency shut-down valves 

that shut when manually tripped or an unsafe condition is sensed)
Simple Control Loop Example - Wrong 

5
Simple Control Loop Example - Right

6

High Pressure

Pneumatic Supply Gas

(15 -35 psig typical) Bleed (Continuous)

or

Vent (Intermittent)

A control loop has the 

following components: 

• Pneumatic supply gas

• Pneumatic controller

• Process variable / 

measurement

• Valve actuator

• Control valve
Simple Process Control Loop Concepts

7

 The sensor, control valve and actuator do not bleed or 

vent gas

 All emissions occur at the controller

 The amount of gas needed for a full actuation cycle 

depends on the pressure and volume of the control loop

 The full actuation volume is the volume of the valve actuator + 

the tubing from the controller to the actuator – corrected to 

standard conditions for the actuation pressure. 

 For a continuous bleed controller the speed of actuation 

is limited by the rate that gas can pass through the 

restrictive orifice. (Limits utility of low bleed devices)
Example: 3-Phase Separator Control Schematic

8

Figure 1 End Device1
Pneumatic Controllers

 Pneumatic controllers convert an input signal to a pneumatic 

pressure output using gas pressure

 Input signals: Mechanical (e.g. float arm (level)), (bordon tube 

(pressure)), (bi-metal rod (temperature), etc)); Electrical (e.g. pressure 

transducer)

 Two types of pneumatic controllers:

 Intermittent vent (physical barrier between supply gas and output)

 Continuous bleed (no physical barrier)

 Two types of service

 On/Off

 Throttling

 Protection/Shut-in Devices – unique category

9
Controller Description

10

 Large number of controller manufacturers and models

 Large number of field configurations

 All typically control a valve via a valve actuator

 From an emissions standpoint, process controllers can be 

classified into 4 buckets

Type of Service

On/Off Throttling

Type of 

Controller

Intermittent Vents on de-actuation with 

emissions near zero between 

de-actuation cycles

Vents some gas pressure 

when valve needs to 

move towards closed

Continuous Bleeds continuously, rate slows 

while process is “on”, but 

average rate is ~constant

Bleeds continuously, rate 

varies with actuation, but 

average rate is ~constant
On/Off Controller Action – Snap acting vs. Proportional

11

 On/Off Controllers can be configured to operate in a “snap-acting” or proportional mode. 

These modes are often confused with the on/off and throttling services but are not 

interchangeable with them.

 Snap-acting is not the same as On/off service

 Proportional acting is not the same as Throttling service 

 On/Off Snap acting (like an on/off light switch)

 Snap acting controllers wait until a set point is reached and then send a full supply pressure signal to the 

valve actuator which fully opens the valve.

 When the low set point is reached, a snap acting controller will fully vent the actuation volume and return 

the valve to fully closed.

 On/Off Proportional (like a light switch with a dimmer)

 A proportional controller will send a partial pressure signal to a valve actuator as the control variable 

reaches the actuation set point. If the control variable continues to increase, the controller will increase 

the pressure signal to the valve actuator until the variable ceases increasing. 

 When a control variable approaches the de-actuation set point a proportional controller will vent a 

portion of the pressure signal from the actuator. As the control variable continues to decrease the 

controller will decrease the vent rate until the actuator loop is fully depressured. 

 This is different than a throttling action and can be thought of as a soft open/close action

 Snap acting vs Proportional action does not normally have a large impact on emissions. 

 For an intermittent-vent controller, a proportional action may vent somewhat less gas on de-actuation than 

a snap-acting controller in the same service.

 For a continuous bleed controller emissions would be essentially the same between proportional and 

snap-acting settings
Intermittent Controllers – How they operate

12

 On/Off service

 Operate against a set point (s) (e.g. liquid level Hi/Lo)

 Send a pressure signal (gas) when a set point (e.g. liquid level) is 

reached (e.g. pressure-to-open dump valve) to fully open valve

 Vent pressure (gas) to fully return valve to prior position (e.g. 

normally closed with spring-for-return dump valve)

 Throttling service (like cruise control in your car)

 Operate against a desired set point (e.g. pressure)

 Send a pressure signal (gas) to increase output signal (pressure to 

open – partially open valve) 

 Vent pressure (gas) to decrease output signal (partially close valve)

 Hold a valve in an intermediate position
Intermittent Controllers – Design & Operation

13

 Typically a pilot (small 3-way valve) operated design

Pilot Ball

Upper Seat

Output Port

Thrust Pin

Supply Port

• To actuate, the thrust pin displaces the upper ball allowing 

supply gas to flow to the output port and valve actuator

• To de-actuate, the thrust pin moves down, the upper ball 

reseats and the exhaust port is opened de-pressuring the 

actuator and tubing

• In throttling service the diaphragm senses force/feedback with 

the output signal proportional to the mechanical force on the 

thrust pin. The upper ball controls supply gas and has spring 

assist to help seating and the lower ball vents gas. The pilot 

seeks to maintain equilibrium by increasing or decreasing 

pressure. Supply air does not flow when balanced.

Exhaust Port Not Shown

Images courtesy

of Norriseal

Diaphragm

Lower Ball

Assist Spring
Intermittent Controllers – Emissions #1

14

 Two components to emissions in normal operation

 Vent on de-actuation – Almost all emissions from an intermittent 

controller are from venting the internal volume from the valve actuator 

to return the valve to its prior position and return the control loop to 

an idle (non-emitting) mode. 

 Seepage/Leakage past pilot ball/seat – Normally minor

 De-actuation vent volume depends on:

 Size/volume of valve actuator & length of valve actuator travel –

Actuation Volume

 Service

• On/Off - Pressure of output gas (function of supply pressure and controller); 

• Throttling – Differential pressure from adjustments to maintain set-point 

 Length and diameter of tubing from controller to actuator
Intermittent Controllers – Emissions #2

15

 Emissions from intermittent controllers are “event based”

 An event is an occurrence of cycling the control valve actuator

 Nearly zero emissions between events

 Gas volume emitted per unit of time depends on frequency of 

cycles and de-actuation volume per cycle

 Total vented gas is a function of the number of times that the 

valve operates, not the length of time the controller is in 

operation

 Normal continuous seepage/leakage depends on:

 Material of balls and seats; Elastomer seats claim zero leakage

 Pressure of supply gas

 Gas gravity; Natural gas volume is ~1.3 X air volume 

 Designed for near-zero emissions when not de-actuating a control loop
Emission Profile

16

On/Off Snap Acting

Throttling

More frequent de-actuations 

with less volume each

Note: data is not actual; constructed for illustration purposes only

0.000

0.050

0.100

0.150

0.200

0.250

0.300 14:44:00 14:44:20 14:44:40 14:45:00 14:45:20 14:45:40 14:46:00 14:46:20 14:46:40 14:47:00 14:47:20 14:47:40 14:48:00 14:48:20 14:48:40 14:49:00 14:49:20 14:49:40 14:50:00 14:50:20 14:50:40 14:51:00 14:51:20 14:51:40 14:52:00 14:52:20 14:52:40 14:53:00 14:53:20 14:53:40 14:54:00 Gas Emitted (SCF/Min)

Minutes and Seconds

Intermittent Controller - On/Off Service

De-actuation Vents

Near-zero leakage

0.000

0.050

0.100

0.150

0.200

0.250

0.300

14:44:0014:44:2014:44:4014:45:0014:45:2014:45:4014:46:0014:46:2014:46:4014:47:0014:47:2014:47:4014:48:0014:48:2014:48:4014:49:0014:49:2014:49:4014:50:0014:50:2014:50:4014:51:0014:51:2014:51:4014:52:0014:52:2014:52:4014:53:0014:53:2014:53:4014:54:00

Gas Emitted (SCF/Minute)

Intermittent - Throttling

De-actuation Vents

Near-zero leakage

Seep/Leak Rate 

examples

Kimray: (Air)

Snap: 0.407 scf/day

Throttle: 0.610 scf/day

Norriseal: (Gas)

Snap: 0.2 scf/hr

Throttle: 0.007 scf/hr

Envirosave: 0.0 scf/hr
Cycle Frequency Challenges

17

 Events do not tend to occur on a predictable schedule

 A pressure regulator is actuated when downstream demand changes (not 

predictable)

 A level controller is actuated when liquids accumulate (a function of the 

process inlet stream which is not completely predictable for a short time 

frame)

 Two identical controllers and end-devices can have significantly 

different emissions depending on the particular process 

configuration, process variable controlled and demands that change 

the number of cycles

 There is no reliable way to convert an event-based emission into a 

time-based emission rate unless the frequency of events (actuations) 

is known or determined. 

 Currently, there is insufficient high-quality measurement data, 

coupled with the relevant process data, to support an average 

emission factor reflective of the population of intermittent 

controller types, services, and conditions. 
Continuous Bleed Controllers 

Design & Operation

18

• As the block/flapper is pushed closer 

to the nozzle the output signal to the 

actuator increases

• As the block/flapper moves away 

from the nozzle the output signal 

decreases

• Maximum emissions are controlled by 

the restriction orifice

Typically a nozzle & flapper arrangement
Continuous Bleed Controllers – How they operate

19

 On/Off service

 Operate against a single set point (e.g. pressure)

 Fully close the nozzle (with flapper) and send a 100% output pressure signal (gas) 

when a set point (e.g. pressure) is reached 

 Continuously bleed gas at a rate determined by critical orifice/restriction size; 

gas pressure; gas gravity and degree of nozzle closure by block/flapper - except 

when nozzle is fully closed 

 Throttling service

 Operate against a desired set point (e.g. pressure)

 Partially close nozzle and send a pressure signal (gas) to increase output signal 

(partially open valve)

 Partially open nozzle to decrease output signal (partially close valve)

 Continuously bleed gas at a rate determined by critical orifice/restriction size; 

gas pressure; gas gravity and degree of nozzle restriction 

 Continuous “low bleed” <6scf/hr; “high bleed” >6scf/hr (regulatory)

 Low bleed rates are achieved by using small diameter orifices (0.012 – 0.009 

inches). These small diameters increase the risk of debris plugging and 

significantly limit the speed of control action/response which limits the situations 

they can be used. 
Continuous Bleed Controllers - Emissions

20

 Emissions in normal operation

 Bleeds to atmosphere continuously except for 100% output (flapper 

fully closes nozzle)

 Rate of bleed decreases during actuation and increases on deactuation

• De-actuation exhausts the actuation volume plus returns controller to 

normal bleed rate

 Bleed rate depends on

 Restrictive orifice size

 Pressure of supply gas

 Gravity of supply gas 

 Lower bleed during actuation depends on degree that flapper closes 

nozzle vs. maximum rate through restrictive orifice

 Exhaust during de-actuation balances lower rate during actuation
Continuous Bleed Controllers

Emission Profile

Note: data is not actual; constructed for illustration purposes only 21

Zero output emission rate 

(steady-state) determined by 

restrictive orifice size, gas 

pressure, and gas properties

0

0.05

0.1

0.15

0.2

0.25

0.3

14:44:0014:44:2014:44:4014:45:0014:45:2014:45:4014:46:0014:46:2014:46:4014:47:0014:47:2014:47:4014:48:0014:48:2014:48:4014:49:0014:49:2014:49:4014:50:0014:50:2014:50:4014:51:0014:51:2014:51:4014:52:0014:52:2014:52:4014:53:0014:53:2014:53:4014:54:00

Gas Emitted (SCF/Minute)

Continuous Low Bleed

Actuation Cycles

De-actuation Exhaust

0

0.05

0.1

0.15

0.2

0.25

0.3

14:44:0014:44:2014:44:4014:45:0014:45:2014:45:4014:46:0014:46:2014:46:4014:47:0014:47:2014:47:4014:48:0014:48:2014:48:4014:49:0014:49:2014:49:4014:50:0014:50:2014:50:4014:51:0014:51:2014:51:4014:52:0014:52:2014:52:4014:53:0014:53:2014:53:4014:54:00

Gas Emitted (SCF/Minute)

Continuous - High Bleed

Actuation Cycles

De-actuation Exhaust

The average emission rate over 

time will be ~equal to the 

amount of gas through the 

restrictive orifice 
Protection/Shut-in Devices/Controllers

22

 Not a source of material emissions

 Used to protect against abnormal 

conditions

 e.g. Overpressure/under-pressure 

(Hi/Lo pilots); Hi/Hi liquid level in 

tanks/vessels; 

 Typically do not emit unless 

abnormal condition occurs

 Example: Hi/Lo pressure pilot

 Normally operates at 100% output 

holding a “fail closed” valve open

 If overpressure or under-pressure 

occurs then output bleeds to 

atmosphere and valve closes

 Not controlling a “process variable”

 Seldom open and emit

Image and information courtesy of FISHER
Intermittent or Continuous – Choice?

23

 Although intermittent vent controllers are the lowest emitting 

selection in most applications, due to not bleeding gas between 

actuation cycles, in certain cases a low bleed continuous type 

controller may be a lower emission selection.

 This is only the case where “over-shooting” the high parameter set point 

can be safely and operationally tolerated.

 Each application must be analysed to determine whether a lowbleed continuous controller is a better emission choice and 

whether the application can tolerate the “overshoot” inherent in 

the slow response time of a low bleed continuous controller. 

 All of the different types and services of controllers have 

scenarios where they are the lowest emission options and 

operators need the flexibility to deploy the appropriate 

technology while taking into account the overriding drivers of 

operational and process safety, stability, and reliability. 
Intermittent or Continuous – Temp. Control Example

24

 Comparing a typical temperature control loop using 

an intermittent controller to a low-bleed continuous 

controller the intermittent is the lower emission 

choice

 Temperature control loops sense temperature and 

control fuel flow to a heater to turn it on or off. 

Very common and basically every field heater 

(dehydrator, tank heater, heater-treater, production 

unit, etc.) has a temperature control loop. Also used 

to control air coolers and other processes 

 Since the fuel valve is small and in low pressure 

service, the actuator used to move the valve is 

equally small volume. For instance an actuator for a 

fuel control valve is about 1.1 cubic inch volume 

which will yield emissions ~100 times smaller per 

cycle than the 110 cubic inch level controller 

example used in background slide.

• It would require ~378 cycles/hr (or about one cycle every 9.5 seconds) to reach 

hourly emissions of 6 scf/hr (regulatory low-bleed continuous). This is not going to 

occur. 

• In this application, an intermittent type controller is the obvious low emission choice 

and fits the process control demand very well. 

Image Courtesy of Kimray
Emission Factors and Population Counts

25

 Subpart W (GHGRP) emission data for pneumatic controllers

 The current emission factor (EF) for intermittent controllers is 

almost certainly an order of magnitude too high. 

 Given how intermittent controllers and continuous controllers operate this is 

almost certainly not valid across the spectrum of controllers and services.

 For 2011 and 2012 the “counts” of pneumatic controllers in each category were 

estimated rather than counted. The 2013 emission data requires an actual count. 

 National inventory emission data for pneumatic controllers

 The National Inventory uses a single estimate of the number of pneumatic 

devices and a single emission factor to calculate a potential methane emission for 

pneumatic controllers (called devices).

 Reductions in emissions attributable to Natural Gas Star voluntary taken and 

reported actions and regulatory required reductions (if required) are subtracted 

from these potential emission estimates.

 It is not clear what the genesis is for the pneumatic controller population 

estimate or emission factor. 
Known Studies/Projects

26

 UT Phase 1 Study sampled 305 controllers.

 UT Phase 2 study, with improved methodologies, is underway and due to be 

published later this year

 GRI/EPA 1996 study

 Canadian Association of Petroleum Producers published pneumatic device 

emission factors (CAPP, 2002 and CAPP, 2003)

 Recent British Columbia study (Prasino) published

 Pioneer Natural Resources is planning to publish the results of a measurement 

study in the near future. 

Important to remember the following:

 All studies need to be QA/QC’d to judge whether the type of controller and 

service was correctly identified 

 All studies need to be QA/QC’d to judge whether the appropriate 

methodologies, sampling populations, and sampling times were used to 

adequately measure emissions from controllers

 All studies need to be QA/QC’d to judge whether the data collected was 

appropriately analyzed and attributed
Conclusions

27

 Operators need the flexibility to deploy the appropriate technology while taking 

into account the overriding drivers of operational and process safety, stability, and 

reliability. 

 Different types and services of controllers have scenarios where they are the 

lowest emission options 

 Intermittent controllers will be the low emission choice in most applications

 In a small number of cases, where the process can tolerate control 

delay, low-bleed continuous controllers may be the low emission choice.

 The current views regarding the emission rate from intermittent controllers 

are almost certainly not correct.

 Although measurement studies are being done and published, care needs to 

be taken to QA/QC the results before simply accepting them. Sufficient good 

quality study and measurement data is not yet available to characterize the 

population of controllers and applications. 

 Due to the methodologies and emission factors the GHGRP and National 

Inventory data for pneumatic controllers needs to be carefully understood 

before using it for either population counts of different types of controllers or 

emissions estimates. 
Background

28
Intermittent Controllers – Emissions Example 

29

 Typical example only. In practice the 

parameters and actuations per unit of 

time will vary. 

 The seepage/leakage of gas (minor) 

while in the idle mode is additional to 

the volume shown

 In 2012 the average US gas well 

produced 1.3 bbls/day of 

oil/condensate (Source: DI)

 In 2012 the average US oil well 

produced 9.4 bbls/day of oil (Source: 

DI)

 In 2012 the average US well produced 

5.6 bbls/day of oil (Source: Basic 

Petroleum Databook)

 At 25 psig and 5.6 bbls/day the gas 

emitted for an average intermittent oil 

dump controller would be between 

1.4 SCF/hr and 0.4 SCF/hr; The 

GHGRP factor is 13.5 SCF/hr

2" Level 

Range

6" Level 

Range

Supply Pressure PSIG 25 25

Atmospheric Pressure PSI 14.7 14.7

Gallons per dump 1.3 3.9

Production/day (bbls) 10 10

Length of tubing (ft) 10 10

Dia. Of tubing (inches) 3/8 3/8

X-section of tubing (sq ft) 0.0008 0.0008

Volume of tubing (scf) 0.022 0.022

Volume of actuator (cubic inches) 110 110

Actuator de-actuation volume (scf) 0.17 0.17

Total volume per cycle (scf) 0.19 0.19

# of Cycles per hour 13.5 4.5

Total volume per hour (scf) 2.6 0.9

On/Off Level Controller/Device Example
Intermittent Controllers – Emission Variability

30

 What can go wrong to increase emissions

 Debris/deposits on vent pilot plug: Material on the vent pilot can 

allow the controller to exhaust gas during the activation cycle. 

 Debris/deposits on the supply pilot plug. Material on the supply pilot 

can cause the introduction of gas while the vent is open.

 Broken spring (when equipped) The spring holds the supply pilotplug on its seat and without this spring the controller has similar 

emissions as a continuous bleed controller. This particular 

malfunction generally calls attention to itself quickly because the enddevice being actuated doesn’t operate.

 Broken diaphragm (where installed). Many intermittent vent 

controllers have diaphragms for various reasons. A detailed analysis 

of a particular device would be required to determine the results of 

the failure on the emitted gas.

 Other - leaking tubing/tubing-fittings, etc (equipment leaks not 

controller emissions) 
Continuous Bleed Controller - Schematic

Schematic Courtesy of FISHER 31
Continuous Bleed Controllers

Emission Variability

32

 What operational factors impact emissions rate

 Supply Gas Pressure and Gravity

 What can go wrong to change emissions

 The orifice can partially plug which lowers bleed rate

 A continuous controller that will still operate an end device 

has its emissions capped by the restriction orifice

 A leak within the controller upstream of the restriction orifice 

can increase total emissions.

 Other (e.g. leaking tubing/tubing-fittings, o-rings)